How credible are hadith when it comes to the historicity of Muhammad?

This is a question people have been asking for centuries – to what degree are we sure that the sayings and doings of Mohammed as recorded in the hadith are accurate reflections of what he actually said and did. It was a challenging issue from the beginning, one Mohammed himself may have acknowledged, if some scholars (e.g., Muhammad Siddiqi) are to be believed, and I agree with them at least in theory.

Briefly, as background for all readers:

The Qur’an is held by most Muslims and certainly by the first Muslims as the inalterable word of God. The Qur’an is not teachings of Muhammed but instead his recitations. The Qur’an says almost nothing about Mohammed specifically (although through textual criticism we could today argue the Qur’an says a great deal about Mohammed, but that’s beside the point). One thing it does say (twice, at least) is that Mohammed is a good model for moral and faithful living. That is, if you want to be a good Muslim, do like Mohammed.

While the degree to which those Qur’anic verses caused early Muslims to want to act like their prophet is probably unknowable, we know for sure that early Muslims were very interested not just in the word of God but in how that influenced the actions of their prophet. Enter: hadith.

Hadith, best translated as “report,” describe Mohammed and his companions and what they had to say about the implementation of Muslim faith. Generally, Qur’an gives you the expectations, hadith tells you how to go about meeting them. Prayer is a great example. The five times a day prayer requirement is not found in Qur’an. It is found in hadith. With this, one of the fundamental components of Muslim practice isn’t said by God at all – it’s from what Mohammed did!

Leading to the very important question – which hadith are true? So we get into the tricky business of isnad, which is at the heart of your question. Isnad is the tracing of authority – which contemporaries of Mohammed said something, how reliable are they known to be, do they disagree with other reliable sources, so forth. By the 9th century, this tracing of authority had evolved into “isnad criticism,” where Muslim scholars were really putting the hadith to task as they compiled them into comprehensive collections.

Our big names in hadith compilation are the 9th century imams Bukhari and his student, Muslim. They worked at a time when Islam was evolving into something larger than a collection of beliefs and rituals -- a legal system. What Mohammed did and said became critical not just for moral living but for the governance of Muslim populations and ultimately for the entire global community of Muslims. So, knowing whether he actually said and did something was vitally important.

Volumes have been filled with how Bukhari and Muslim performed their work, and I won’t get into it other than to say that the general rule is that where Bukhari and Muslim agree on the historical truthfulness of a hadith (that is, someone actually said and did the thing reported), the hadith is considered “sahih” or “sound.” For hadith where they and others are much less sure, they are categorized as hasan (good) or da’if (weak). Good and weak hadith are still a part of the collections, but sahih are taken as accurate and reliable.

And yet, of course, whenever you have people interpreting history, you end up with some modern bias. He may be a bit dated but the Islamic studies scholar Marshall Hodgson argued that during this active era in isnad criticism there were Muslim scholars who straight up invented isnads (as well as hadith) but with an altruistic purpose, quoting Hodgson: “for they assumed…whatever was true and of value for Muhammad’s community must have been said by Muhammad.”

Creative additions were not unique to hadith. We see substantial bias and “creative history” in other moderately contemporary works concerning Muhammed, such as the Sirah, generally called a biography of Muhammed, which most scholars do not take as historically accurate given its history of revisions. By this, understand that the hadith and other works were canonized to a degree in the context of interested parties, politics, and laws, as well as religious belief.

Scholars in the centuries after Bukhari and Muslim have identified hadith where they think the two were incorrect in assessing reliability. The debate goes on. Whereas Qur’an can never be changed according to Muslim belief, hadith are up for interpretation. Which is perhaps the only answer to your question. How do we know which hadith are true? We don’t, not really. We have to rely on historians of antiquity who lived closer to the time of Mohammed and by that hope that they had better sources than we do today. I tend to think they did.

Some reading:

Muhammad Zubayr Siddīqī, Hadīth Literature: Its Origin, Development, Special Features and Criticism

Marshall Hodgson. The Venture of Islam: Conscience and History in a World Civilization