Language:
كتاب الأدب
78  
Good Manners and Form (Al-Adab)
(67)
Chapter: The establishment of a bond of brotherhood and the conclusion of a treaty
(67)
باب الإِخَاءِ وَالْحِلْفِ
Sahih al-Bukhari 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."

حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا يَحْيَى، عَنْ حُمَيْدٍ، عَنْ أَنَسٍ، قَالَ لَمَّا قَدِمَ عَلَيْنَا عَبْدُ الرَّحْمَنِ فَآخَى النَّبِيُّ صلى الله عليه وسلم بَيْنَهُ وَبَيْنَ سَعْدِ بْنِ الرَّبِيعِ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏ "‏ أَوْلِمْ وَلَوْ بِشَاةٍ ‏"‏‏.‏
Reference : Sahih al-Bukhari 6082
In-book reference : Book 78, Hadith 110
USC-MSA web (English) reference : Vol. 8, Book 73, Hadith 105
  (deprecated numbering scheme)