Musannaf Ibn Abi Shayba 27:714

Ibn Idris narrated to us, from Muhammad ibn Ishaq, from ‘Asim ibn ‘Umar ibn Qatadah, from Mahmud ibn Labid, from Abu Sa’id al-Khudri, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "If the people were to travel through a valley or a mountain pass, and you were to travel through a valley or a mountain pass, I would travel through your valley and your mountain pass. You are the inner garment (shi’ar), and the people are the outer garment (dithar). And were it not for the migration (Hijrah), I would have been a man from the Ansar." Then he raised his hands until I could see the whiteness of his armpits, from beneath his shoulders, and said: "O Allah, forgive the Ansar, and the children of the Ansar, and the children of the children of the Ansar."