Musnad Ahmad 5:225

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, my father Ishaq ibn Yasar narrated to me, from Miqsam Abu al-Qasim, the freed slave of Abdullah ibn al-Harith ibn Nawfal, from his master Abdullah ibn al-Harith, who said: I performed Umrah with Ali ibn Abi Talib during the time of Umar or the time of Uthman. He stayed with his sister, Umm Hani bint Abi Talib. When he finished his Umrah, he returned, and water was poured for him to bathe, so he bathed. When he finished his bath, a group of people from the people of Iraq entered upon him and said: "O Abu al-Hasan, we have come to you to ask you about a matter we would like you to inform us about." He said: "I suppose al-Mughirah ibn Shu'bah is telling you that he was the person most recently in the company of the Messenger of Allah, may Allah bless him and grant him peace?" They said: "Yes, that is what we came to ask you about." He said: "The person most recently in the company of the Messenger of Allah, may Allah bless him and grant him peace, was Qutham ibn al-Abbas."