Musnad Ahmad 12:3

'Arim and 'Affan narrated to us, they said: Mu'tamir ibn Sulayman narrated to us. 'Affan said in his narration: He said: I heard my father, Abu 'Uthman narrated to us, that 'Abd al-Rahman ibn Abi Bakr narrated to him, that the people of the Suffah were poor people. And the Messenger of Allah (peace and blessings of Allah be upon him) said one time: "Whoever has food for two, let him take a third"—and 'Affan said: "or three"—"and whoever has food for four, let him take a fifth or a sixth"—or as he said. And Abu Bakr came with three, and the Prophet (peace and blessings of Allah be upon him) went with ten, and Abu Bakr with three—'Affan said: "with a sixth."