Musnad Ahmad 32:2043

'Affan narrated to us, Hammad ibn Salamah narrated to us, 'Asim al-Ahwal narrated to us, from Anas ibn Malik, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) established a bond of brotherhood between the Emigrants (Muhajirun) and the Helpers (Ansar) in the house of Anas ibn Malik."