Musnad Ahmad 21:4

'Abdullah ibn Bakr narrated to us, Hatim—meaning Ibn Abi Saghir—narrated to us, some of the sons of Al-Muttalib narrated to me, he said: 'Ali ibn 'Abdullah ibn 'Abbas came to us during one of those seasons [of Hajj]. He said: I heard him saying: My father, 'Abdullah ibn 'Abbas, narrated to me, from his father, Al-'Abbas, that he came to the Messenger of Allah (may Allah bless him and grant him peace) and said: "O Messenger of Allah, I am your uncle, my age has increased, and my appointed time has drawn near, so teach me something by which Allah may benefit me." He said: "O 'Abbas, you are my uncle, and I will not avail you anything against Allah. But ask your Lord for pardon and well-being in this world and the Hereafter." He said it three times. Then he came to him at the turn of the year, and he said the same thing to him.