Sahih al-Bukhari, Volume 8, Book 73, Hadith 105 (USC-MSA) ⓘ
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."
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 " .
also referenced under: Book 78, Hadith 110 (In-Book) & Hadith 6082 (DarusSalam)