What is your opinion about a matter which the Messenger of Allah (ﷺ) did but you forbid it? Thereupon Uthman said: You leave us alone, whereupon he ('Ali) said: I cannot leave you alone. When 'Ali saw this, he put on Ihram for both of them together (both for Hajj and 'Umra).
Sahih Muslim Book 15, Hadith 173