From Sahih Bukhari (Hadith 6082):
Narrated Anas:When `Abdur-Rahman came to us, the Prophet (ﷺ) established a bond of brotherhood between him and Sa`d bin Ar-Rabi`. Once the Prophet (ﷺ) said, "As you (O `Abdur-Rahman) have married, give a wedding banquet even if with one sheep
Reference: Bukhari 6082