Musnad Ahmad 1:76

Yahya ibn Hammad narrated to us, Abu 'Awanah narrated to us, from al-A'mash, from Isma'il ibn Raja', from 'Umayr, the freed slave of al-'Abbas, from Ibn 'Abbas, who said: When the Messenger of Allah (peace and blessings of Allah be upon him) passed away and Abu Bakr was made caliph, al-'Abbas disputed with 'Ali regarding things that the Messenger of Allah (peace and blessings of Allah be upon him) had left behind. Abu Bakr said: "A thing that the Messenger of Allah (peace and blessings of Allah be upon him) left, and he did not move it, I will not move it." When 'Umar was made caliph, they disputed before him. He said: "A thing that Abu Bakr did not move, I will not move it." He said: When 'Uthman was made caliph, they disputed before him. He said: 'Uthman remained silent and lowered his head. Ibn 'Abbas said: I feared that he might take it, so I struck my hand between the shoulders of al-'Abbas and said: "O father, I adjure you to surrender it to 'Ali." He said: So he surrendered it to him.