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).

اجْتَمَعَ عَلِيٌّ وَعُثْمَانُ ؓ بِعُسْفَانَ فَكَانَ عُثْمَانُ يَنْهَى عَنِ الْمُتْعَةِ أَوِ الْعُمْرَةِ فَقَالَ عَلِيٌّ مَا تُرِيدُ إِلَى أَمْرٍ فَعَلَهُ رَسُولُ اللَّهِ ﷺ تَنْهَى عَنْهُ فَقَالَ عُثْمَانُ دَعْنَا مِنْكَ فَقَالَ إِنِّي لاَ أَسْتَطِيعُ أَنْ أَدَعَكَ فَلَمَّا أَنْ رَأَى عَلِيٌّ ذَلِكَ أَهَلَّ بِهِمَا جَمِيعًا

I saw ʿAli and ʿUthman ؓ between Makkah and Madinah. ʿUthman was telling people not to do tamattuʿ or join them together (Hajj and ‘Umrah, i.e., qiran). When ʿAli ؓ saw that, he entered ihram for both of them together and said: Here I am for ʿUmrah and Hajj together ‘Uthman ؓ said: You see me telling the people not to do that and you do it? He said: I will not give up a Sunnah of the Messenger of Allah ﷺ for the opinion of anyone among the people. (Using translation from Aḥmad 1139)

أَنَّهُ شَهِدَ عَلِيًّا وَعُثْمَانَ بَيْنَ مَكَّةَ وَالْمَدِينَةِ وَعُثْمَانُ يَنْهَى عَنِ الْمُتْعَةِ فَلَمَّا رَأَى ذَلِكَ عَلِيٌّ أَهَلَّ بِهِمَا جَمِيعًا فَقَالَ «لَبَّيْكَ بِحَجَّةٍ وَعُمْرَةٍ مَعًا» فَقَالَ تَرَانِي أَنْهَى عَنْهُ وَتَفْعَلُهُ فَقَالَ «لَمْ أَكُنْ لِأَدَعَ سُنَّةَ رَسُولِ اللَّهِ ﷺ بِقَوْلِ أَحَدٍ مِنَ النَّاسِ»

[Machine] Ali has whatever you want of a matter that the Messenger of Allah ﷺ did and you forbid? He said: Leave us from you. He said: Indeed, I cannot leave you. So when Ali saw that, he embraced them all.

لَهُ عَلِيٌّ مَا تُرِيدُ إِلَى أَمْرٍ فَعَلَهُ رَسُولُ اللهِ ﷺ تَنْهَى عَنْهُ؟ قَالَ دَعْنَا مِنْكَ قَالَ إِنِّي لَا أَسْتَطِيعُ أَنْ أَدَعَكَ فَلَمَّا رَأَى ذَلِكَ عَلِيٌّ أَهَلَّ بِهِمَا جَمِيعًا