Marwan bin Hakam reported,
I witnessed Uthman and Ali 
, and Uthman was forbidding tamattu and combining the two together. When Ali saw this, he entered into ihram for both, saying, "Labbayk for an Umra and a Hajj." He then said, "I will not abandon the sunnah of the Prophet ﷺ for anyone's statement."
Azami 4935
Sahihعن مروان بن الحكم، قال
شهدت عثمان وعليا رضي الله عنهما، وعثمان ينهى عن المتعة وأن يجمع بينهما، فلما رأى علي أهل بهما لبيك بعمرة وحجة قال: ما كنت لأدع سنة النبي ﷺ لقول أحد.
Bukhari narrated it in "Hajj" (1563) through Shuba, from Hakam, from Ali bin Husayn, from Marwan, with the same wording.Bukhari also narrated it (1569), and Muslim in "Hajj" (1223), through Shuba, from Amr bin Mura, from Saeed bin Musayab, who said, Ali and Uthman met at Usfan, and Uthman used to forbid combining Umrah with Hajj. Ali said to him, "Why do you want to forbid something the Messenger of Allah ﷺ himself did?" Uthman said, "Leave us out of this!" Ali replied, "I cannot leave you be." When Ali saw this, he declared his intention to perform both together. The wording given here is Muslim's.Muslim also narrated it through Shuba, from Qatada, who said, Abdullah bin Shaqiq said, "Uthman used to forbid combining Umrah with Hajj, while Ali used to command it. Uthman said something to Ali, then Ali said, 'You surely know that we performed it in this manner with the Messenger of Allah ﷺ?' Uthman said, 'Yes, but we were afraid.'"