Musnad Ahmad 32:1969

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, and Hajjaj narrated to us, he said: Shu'bah narrated to me, he said: I heard Qatadah narrating from Anas, he said: The Messenger of Allah, peace and blessings of Allah be upon him, gathered the Ansar and said: "Is there anyone among you who is not of you?" They said: "No, except a son of a sister of ours." The Messenger of Allah, peace and blessings of Allah be upon him, said: "The son of a sister of a people is one of them." Hajjaj said: Or "is from themselves." He then said: "Verily, the Quraish are recent in their departure from Jahiliyyah (pre-Islamic ignorance) and calamity, and I intend to console them and reconcile them. Are you not pleased that the people return with the world, while you return with the Messenger of Allah to your homes? If the people were to travel through a valley, and the Ansar were to travel through a mountain pass, I would travel through the mountain pass of the Ansar."