ʿUthman used to forbid mut’ah (of Hajj, i.e., tamattuʿ) and ‘Ali used to enjoin it. ʿUthman said something to ʿAli, then ʿAli said: You know that we did tamattuʿ with the Messenger of Allah ﷺ . He said: Yes, but we were in a state of fear then.
عَلِيٌّ لَقَدْ عَلِمْتَ أَنَّا قَدْ تَمَتَّعْنَا مَعَ رَسُولِ اللهِ ﷺ؟ قَالَ أَجَلْ وَلَكِنَّا كُنَّا خَائِفِينَ