Needless to say, there's that much evidence of African slaves practicing Islam in the Americas because it was not something those who did practice would've spoken about, and thus would've made it into records. But, that doesn't mean there's no evidence, indeed some did speak about it, and practitioners left a good amount of evidence of their beliefs if we know where to look. When we first see them referenced in records it is because Europeans were deeply frightened by the possibility of their revolting, and for good reason - the first reference is in 1503 when the governor of Hispaniola wrote to Queen Isabella of Spain that they should stop importing Muslim slaves. And on Christmas morning 1522, that issue came back to bite them in the culo when 20 Muslim Wolof slaves rose up on Hispaniola in the first slave revolt recorded in the Americas.
From Practical Rules for the Management and Medical Treatment of Negro Slaves in the Sugar Colonies (1803), its author notes that Muslims "are excellent for the care of cattle and horses [speaking about Fulani people]..." and that while working "Many of them converse in the Arabic language." In the early 1800's, a Georgia slaveowner tried to revolutionize slavery by advocating that they should make "professors of the Mahommedan religion...[into] drivers, or influential negroes", and cited Muslim slaves who sided with the Americas against the British in the War of 1812 as further evidence of their reliability.
Perhaps the most notable example of a practicing Muslim African in the Americas is of Ibrahima abd al-Rahman, a son of Emir Ibrahima Sori, a noble of the Muslim theocratic state of Futa Jallon in what is now Guinea. Al-Rahman was captured in war in 1788 (he was 26) and was sold a few times ending up in Natchez, Mississippi. His owner Thomas Foster called him Prince. In 1826 (now aged 64) the American Colonization Society discovered his situation and thought he was a great candidate for furthering their goals - convincing Americans to send Africans back, both to end the problem of slavery but also to racially purify their new country. When he spoke to ACS leaders, he told them he was (still) a Muslim. The ACS pressured his owner to free him which he eventually did, but without freeing al-Rahman's family. Considering he wasn't going to walk away without them, he then toured northern cities in a fundraising publicity stunt so he could eventually pay for their release. During these stunts, he wore (was made to wear?) "Moorish" clothing to enhance his exoticism, and for donations he would write al-Fatiha (the opening of the Quran) on pieces of paper; so obviously after some 40 years the memories had not faded.
As Commustar notes in an answer about slave revolts...
Another example would be the Bahia revolt in 1835. In the decade before the revolt, that area of Brazil saw a large influx of slaves, including a large number of Muslim Yoruba slaves. In court depositions after the revolt, participants told how they would meet together to eat, as part of a custom to eat meals prepared by Muslim hands. Additionally, behind closed doors participants would wear an [abaya], which is a white shirt or frock. During the revolt, participants wore the [abaya] in order to identify their co-conspirators.
Certainly, there were participants in the Bahia revolt that were not ethnic Yorubas, but these depositions do demonstrate how communities could maintain their religious identity in Brazil in secret.
Artifacts which corroborate these slim records are incredibly rare, but some have been found. The one that I'm thinking of is a small metal charm which features the phrase "No God But Allah" in Arabic. It was found at Fort Shirley, Pennsylvania, and dates to ca. 1760; now at the Museum of the American Revolution in Philadelphia. It has a small hole drilled in the top so it was intended to be worn as a necklace pendant, surely worn under one's clothing. And so this small object's use mirrors the history of African Islam in the Americas - it was held close the heart and hidden from view; so no wonder it is so difficult to find this in the historical record.
Muslims Lived in America before Protestantism even Existed, by Sam Haselby
To what degree did African slaves maintain their identities? answer by u/Commustar
What elements of African culture survived in the Americas? answers by u/firedrops & u/itsallfolklore
There's already a fine answer by /u/Antiquarianism ; I wanted to mention a smaller and lesser known avenue of Islam to the Americas that - while not on Africans - seems relevant : crypto-Muslims or "moriscos " who had been expelled from Spain.
(From earlier answers of mine) The Jewish conversos in Latin America have been studied in much more detail than the Muslims or converted Muslims (aka moriscos) in Spanish America. Katherina P. Cook has sorta recently written an interesting book about them, "Forbidden Passages: Muslims and Moriscos in Colonial Spanish America ". In it she argues that despite laws prohibiting passage to the Americas to moriscos (and Jews/conversos), there were still many cases of illegal migration ( as with conversos). Cook relies mostly on judicial documents, and at least to me it seems that it's still hard to get a sense of numbers for these forbidden crossings - though certainly nowhere near the huge forced migration of Africans to slavery . We do know that they took place during the 16th and 17th centuries at least.
It also seems that periods of special hardship for the Spanish morisco communities led to more emigration. Muslims in Andalusia had been forced to convert a few years after the fall of Granada in 1492, but were periodically persecuted for practising "crypto-Islam". The second rebellion (ie war) of the Alpujarras from 1569-72 was a major crisis influencing migration, and similarly the expulsions of all moriscos from Spain from 1609 onwards led to further massive migrations to Norther Africa, the Ottoman empire, but also to the Americas. Cook mentions cases of moriscos migrating first to North Africa and from there to Spanish America - presumably due to hostile attitutes against them in the Maghreb.
Another interesting aspect is the self-identification of moriscos in Spanish America. On the one hand there were cases of moriscos going before colonial courts to argue that they were Old Christians, and that their early conversion in Spain gave them the rights of Christians in the Americas. On the other hand the inquisition was not responsible for Muslims in Spanish America, and there were also cases of moriscos arguing for their "muslim-ness", probably to escape perscution through the inquisition as moriscos. Just to note that drawing on lineage (as with the Old Christians) was a central part of identification in early modern Spain and Spanish America which influenced the development of the casta system; and that this casta system was at least early on not yet so fixed, so that people could change from one group to another.
Cook discusses some very interesting examples of court cases, including that of Diego Herrador, “a shoemaker residing in Mexico City,” who in 1577 was charged with concealing his morisco heritage on his mother’s side to obtain a false licence” to enter the Americas in spite of the travelling ban. Another case is that of Nicolás de Zamudio Oviedo, who in Lima in 1636 accused a local priest of publicly calling him a “Morisco, drunken dog,” but whose case collapsed “because of the lack of willing witnesses to testify against a priest”. Cook also mentions moriscos being accused of sorcery or of using Islamic symbols in religious rituals. This points to occupations for moriscos as healers, diviners, practioners of magic and similiar professions. These they would have shared with Africans and native people, who would often take part in a "shadow economy" because other positions would not have been attainable - including more visible/wealthy positions as traders as you mention.
So we definitely have a smaller presence of "crypto-Muslims" or moriscos in early modern Spanish America in addition to the African Muslims, although their exact numbers and influence are harder to gauge. Nonetheless this presence presented a major challenge for the Spanish Crown, since its legitimisation for ruling parts of the Americas rested on the empire's Christianity:
The presence of Moriscos and their descendants would undermine missionary activities and delegitimize Spanish claims and title to lands in the Western Hemisphers. When faced with similarly racializing discourses from Protestant European rivals labeling Spain a Moorish nation, some Spanish writers responded by rewriting their histories and emphasizing ancient Christian genealogies and descent from the Goths rather than intermixture with Muslims. [Cook, 189-90]
Lastly, Cook also discusses Spanish fears of the immigration of Muslims from the Philippines, another Spanish overseas possession in the 16th century; as well as fears of New Christians (esp. conversos) being brought from Brazil to Spanish America, with exile a common form of punishment in Portuguese America.
Cook also addresses the crossings. What's certain is that emigration would have been easier until the mid-16th century, when racial attituted and emigration laws were becoming harsher. Before then it was still possible e.g. for slaveholders to bring Muslim or morisco slaves to the Americas; and possible that elite moriscos emigrated with more ease. But even in the latter 16th century there were still possibilities:
Falsifying papers, escaping as soldiers or sailors, and paying for space to accompany officials to the Americas, all provided some of the means by which individuals slipped unnoticed into the New World. Once in the Americas, clandestine emigrants faced authorities who found it challenging to oversee who was settling in the new viceroyalties, even as they were mapping out jurisdictions and attempting to follow up on the royal decrees.
Such "loopholes"
... provided opportunities for new Christians to attempt to forge new lives in the Spanish Americas, as they could not in Spain, where peninsular controls were tighter. [Cook, 79]
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I wrote a longer thing here on the moriscos in Europe, who migrated also especially to Northern Africa and the Ottoman empire in this period, spelling the end of (crypto)-Islam in Western Europe:
I just want to underscore that there's actually quite a lot of evidence of Islamic practice among West Africans taken across the Atlantic. Several monographs to consult:
Diouf, Sylviane. Servants of Allah: African Muslims Enslaved in the Americas. New York: New York University Press, 2013.
African Muslims in Antebellum America : Transatlantic Stories and Spiritual Struggles . [Rev. and updated ed.]. New York: Routledge, 1997.
Einboden, Jeffrey. Jefferson’s Muslim Fugitives: The Lost Story of Enslaved Africans, Their Arabic Letters, and an American President. New York: Oxford University Press, 2020. (Just published: I haven't read it yet.)
There's also a reason why the prevalence of Islamic practice in slave communities is hard to determine beyond the general lack of interest among New World slaveholders in recording or observing the day to day lives and thoughts of enslaved Africans. Essentially, Mande, Wolof, Fulani and other groups who were more likely to be practicing Muslims were more predominant in the early Atlantic slave trade, and at that time, in many of their societies, Islam was still an elite or court religion, though aspects of Islamic worship and practice had often been incorporated in syncretic ways into indigenous spiritual practice. We have much less information about the small numbers of Africans brought to the earliest Atlantic communities in the Americas in the 1600s, and their practices were more mixed with and overlaid by the cultures, languages and ideas of later West and Central African arrivals. The huge wave of people brought over in the mid- to late-1700s and early 1800s were more predominantly from Atlantic Africa between present-day Ghana and present-day Nigeria and fewer of them were practicing Muslims--though by the late 1700s, Islam had also become far more widespread in Senegambia, the Upper Guinea region and the Hausa city-states north of the Oyo Empire. It's much easier to trace specific religious connections between Yoruba, Fon, Akan, Igbo etc. practices and the New World because those groups were so much more heavily represented at the height of the Atlantic slave trade.