Abu Dawud Book 12, Hadith Number 2920.
Chapter : Alliance.
Narated By Anas b. Malik : The Apostle of Allah (PBUH) established an alliance (of brotherhood) between the Emigrants and the Helpers in our house. He was asked: Did not the Apostle of Allah (PBUH) say: There is no alliance in Islam? He replied: The Apostle of Allah (PBUH) established an alliance between the Emigrants and Helpers in our house.