Abu Dawud
Oaths and Vows
Book Number: 015 / Hadith Number: 3250
Narated By Suwayd ibn Hanzalah : We went out intending (to visit) the Apostle of Allah (pbuh) and Wa'il ibn Hujr was with us. His enemy caught him. The people desisted from swearing an oath, but I took an oath that he was my brother. So he left him. We then came to the Apostle of Allah (pbuh), and I informed him that the people desisted from taking the oath, but I swore that he was my brother. He said: You spoke the truth: A Muslim is a brother of a Muslim.