Sahih Bukhari
Transferance of a Debt from One Person to Another (Al-Hawaala)
Volume: 003 / Book Number: 037 / Hadith Number: 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."