Musannaf Ibn Abi Shayba 27:303

Zayd ibn al-Hubab narrated to us, from Musa ibn Ubaydah, who said: Abu Mu’adh informed me, from Khattab—or Abu al-Khattab—from Ali, who said: While I was sitting with the Messenger of Allah (peace and blessings of Allah be upon him), Abu Bakr and Umar approached. He said: "O Ali, these two are the masters of the middle-aged men of the people of Paradise, except for what pertains to the prophets. So do not inform them."