First, finally, something I can answer!

Unfortunately, the honest answer is no, there has never been a unified pan-Abrahamic alliance.

That said, it'd be wrong to say that Abrahamic religions have never combined arms to fight against a common enemy under the guise of such an alliance.

Case in point: the German-Ottoman alliance in WW1.

German-Ottoman relations existed since the founding of the German Empire (the German Orient Society had regularly hosted Ottoman dignitaries since its founding in 1845), but picked up considerable steam at the onset of the 20th century. Realizing that a colonial conflict with Great Britain was almost inevitable, German Emperor Wilhelm II determined in 1905 that Germany ought not to enter into a war with Britain until it had formalized an alliance with the Ottoman Empire saying "we ought not to proceed until our alliance with Islam is perfected”.

This policy mostly stems from a report issued by a German consular official based in Cairo, Max von Oppenheim, who spoke in favor of utilizing the Ottoman's official foreign policy doctrine of "pan-Islamism" for Germany's favor. This of course was almost a perfect foil of British colonial policy, which had put millions of Muslims under British colonial rule, and was contrasted with German colonies which had very small Muslim populations. An aside: If you're interested in a colorful historical figure, Max von Oppenheim certainly fits the bill (He often wore traditional Arab attire, and actively participated in student intrigue, mostly regarding overthrowing British colonial rule, at Al-Azhar University in the early 1900s).

Germany and the Ottoman Empire finalized their alliance on August 2, 1914, and the Ottoman Empire (militarily) entered WW1 on October 29, 1914, by bombing Russian targets in the Black Sea.

The closest the German and Ottoman Empire came to declaring a pan-Abrahamic alliance was the Ottoman Empire’s declaration of Jihad against the British, French, and Russian Empires. This document, prepared in the form of 5 legal opinions, signed by 29 religious authorities, and blessed by the Sultan himself was presented to the Ottoman elite on November 11th and then, during a pro-war rally, was read aloud on Saturday, November 15th, 1914 in Istanbul. Post-war scholarships largely focused on Germany’s role in the Ottoman Empire’s declaration of Jihad, but recent scholarship largely credits the Ottomans themselves for the declaration of Jihad, something that is supported the Ottoman’s often enthusiastic declaration of Jihad in other 19th century conflicts that Germany had nothing to do with.

An interesting tidbit that ties to this question comes from Jihad and Islam in World War I, published by the Leiden University Press: “In the Ottoman world, one did not even have to be Muslim to wage jihad. For the early Ottoman period,… there’s a situational character and fluidity of the ways in which the concept Jihad was employed… simply rendered into English as “holy war.” “Holy by no means meant “in line with Islamic law” and that, perhaps counter to our modern expectations. [For example], a Christian corsairs – or an Armenian prince and a Greek princess, for that matter – could be featured in epics and stories as warrior heroes fighting shoulder to shoulder with Muslims.”

This is an important distinction to today’s interpretation of Jihad because the declaration of Jihad by the Ottoman Empire singled out specifically the British, French, and Russian Empires. There’s no direct mention of German, Austrian, or Hungarian powers in that declaration, but one could make a strong argument that the Jihad declared by the Ottoman Empire was Jihad being waged by not just Muslims but by Germans, Austrians, etc. together with the Ottoman Empire.

As the war progressed (and not for the better), German and Ottoman war departments increasingly relied on religious propaganda to boost sagging war morale in their respective countries.

An example: the Leipziger Neuesten Nachrichten, a Germany Daily in Leipzig wrote in late 1916,"There rises up before England's sunken eyes the spectre of the exaltation of all Islam", "a call from the Caliph, and it will be heard as far as Arabia, in Algiers, in Morocco, and the band of shared faith with unite them all.”, a direct reference to the Jihad declared by the Ottoman Empire.

Similarly, a brochure (“Die Wahrheit über den Glaubenskrieg”, The Truth about the War of Belief) authored by Salih ash-Sharif at-Tunisi, a religious scholar of North African origin, provides a religious casus belli for the Great War from both an Ottoman and German perspective. Highlighting WW1 as a war against unrighteous enemies, Salih ash-Sharif at-Tunisi argued that it was the personal duty of all Muslims to enter the fight against the Russian, French, and British colonizers. The German Society for Islamic Studies actively attempted to spread Salih ash-Sharif at-Tunisi’s work widely in both the Ottoman and German Empires.

This is all to say: while there’s never been a true unified pan-abrahamic alliance, the German Empire and Ottoman Empire certainly tried to create the perception of one during WW1.

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Aksakal, Mustafa. “'Holy War Made in Germany'? Ottoman Origins of the 1914 Jihad.” War in History, vol. 18, no. 2, 2011, pp. 184–199. JSTOR, www.jstor.org/stable/26098597. Accessed 26 Feb. 2021.

McKale, Donald M. “Germany and the Arab Qustion Before World War I.” The Historian, vol. 59, no. 2, 1997, pp. 311–325. JSTOR, www.jstor.org/stable/24449971. Accessed 26 Feb. 2021.

Zürcher, Erik-Jan. Jihad and Islam in World War I: Studies on the Ottoman Jihad on the Centenary of Snouck Hurgronje’s “Holy War Made in Germany” (Debates on Islam and Society). Leiden University Press, 2016.