Musannaf li Ibn Abi Shaybah (25 vol)المصنف لابن أبي شيبة

Compiled by the great scholar Ibn Abi Shaybah al-Absi al-Kufi (d. 235 AH), this work is a monumental encyclopedia of early Islamic tradition. It predates the "Six Authentic Books" (including Sahih Bukhari and Muslim) and serves as a primary source for understanding the development of Islamic law and theology.

The Musannaf is prized for its preservation of the legal opinions and historical reports of the first three generations of Islam. It covers a vast range of subjects, including acts of worship, transactions, ethics, and historical biographies (Maghazi). It is often considered a "treasure trove" for researchers because it provides the raw material of early Islamic thought before it was codified into the major schools of jurisprudence.