Conversation so far:
What was unusual about Schacht's method?
As a whole, Origins critiques the methods and standards of ḥadīth verification, an early and centrally important stage in the formation of Islamic jurisprudence.
What is one of the sources of Islamic law?
The Quran

Question: What other sources did he say Islamic law comes from?
Self-contained rewrite: What other sources did Joseph Schacht say Islamic law comes from besides the Quran?