Musnad Abu Ya'la al-Mawsili 115:161

Abu Musa narrated to us, Muhammad bin Ja'far narrated to us, Shu'bah narrated to us, he said: I heard Qatadah narrating from Anas, who said: The Messenger of Allah (ﷺ) gathered the Ansar and said: "Is there anyone among you who is not of you?" They said: "No, except for a son of our sister." The Messenger of Allah (ﷺ) said: "The son of a sister of a people is one of them." He then said: "Indeed, the Quraish are recent in their departure from Jahiliyyah and [have suffered] a calamity, and I intend to console them and reconcile them. Are you not pleased that the people return with worldly goods, 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."