Sahih Muslim
The Book of Pilgrimage (Kitab Al-Hajj)
Book Number: 007 / Hadith Number: 2815
'Abdullah b. Shaqiq reported that 'Uthman (Allah be pleased with him) used to forbid Tamattu', whereas 'Ali (Allah be pleased with him) ordered to do it. 'Uthman said a word to 'Ali, but 'Ali said: You know that we used to perform Tamattu' with the Messenger of Allah (may peace be upon him), whereupon he said: It is right, but we entertained fear. This hadith has been narrated by Shu'ba with the same chain of transmitters.