Sahih Muslim Book 7, Hadith Number 2815.

Chapter : Permissibility of the Tamattu’ (form of pilgrimage).

‘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.