Narrated Asim: I heard Anas bin Malik, "Have you ever heard that the Prophet said, 'There is no alliance in Islam?' " He replied, "The Prophet made alliance between Quarish and the Ansar in my house."
— Sahih Bukhari, Volume 3, Book 37: Transferance of a Debt from One Person to Another (Al-Hawaala), Hadith #491