(11) باب تَزْوِيجِ الصِّغَارِ مِنَ الْكِبَارِ
Narrated 'Urwa:
The Prophet (ﷺ) asked Abu Bakr for `Aisha's hand in marriage. Abu Bakr said "But I am your brother." The Prophet (ﷺ) said, "You are my brother in Allah's religion and His Book, but she (Aisha) is lawful for me to marry."
Reference: Sahih al-Bukhari 5081
In-book reference: Book 67, Hadith 19
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 7, Book 62, Hadith 18