Transferance of a Debt from One Person to Another (Al-Hawaala)

Bukhari :: Book 3 :: Volume 37 :: Hadith 491

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."