Wedlock, Marriage (Nikaah)

Bukhari :: Book 7 :: Volume 62 :: Hadith 18

Narrated 'Ursa:

The Prophet asked Abu Bakr for 'Aisha's hand in marriage. Abu Bakr said "But I am your brother." The Prophet said, "You are my brother in Allah's religion and His Book, but she (Aisha) is lawful for me to marry."