Musnad Ahmad 3:34

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Qatadah, who said: ‘Abdullah ibn Shaqiq said: ‘Uthman used to forbid the *mut‘ah* (temporary marriage/pilgrimage), and ‘Ali used to command it. So ‘Uthman said something to ‘Ali, then ‘Ali said: "You know that we performed *mut‘ah* with the Messenger of Allah, may Allah bless him and grant him peace." He said: "Yes, but we were fearful."