Sahih Muslim Book 1, Hadith Number 302.

Chapter : The beginning of Revelation to the Messenger of Allah (may peace be upon him).

This hadith has been narrated on the authority of ‘Aisha with another chain of narrators like one transmitted by Yunus, i.e. the first thing with which the revelation was initiated with the Messenger of Allah (may peace be upon him) except the words: By Allah, Allah would never humiliate you, and Khadija said: O son of my uncle! Listen to the son of your brother.