Sahih Bukhari
Good Manners and Form (Al-Adab)
Volume: 008 / Book Number: 073 / Hadith Number: 105
Narrated Anas:
When 'Abdur-Rahman came to us, the Prophet established a bond of brotherhood between him and Sa'd bin Ar-Rabi'. Once the Prophet said, "As you (O 'Abdur-Rahman) have married, give a wedding banquet even if with one sheep."