Sahih al-Bukhari 5081
Sahih al-Bukhari · Book 67: Wedlock, Marriage (Nikaah) · The marrying of young lady to an elderly man
Narrated 'Urwa:
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ ، حَدَّثَنَا اللَّيْثُ ، عَنْ يَزِيدَ ، عَنْ عِرَاكٍ ، عَنْ عُرْوَةَ ، أَنَّ النَّبِيَّ صلى الله عليه وسلم خَطَبَ عَائِشَةَ إِلَى أَبِي بَكْرٍ فَقَالَ لَهُ أَبُو بَكْرٍ إِنَّمَا أَنَا أَخُوكَ، فَقَالَ " أَنْتَ أَخِي فِي دِينِ اللَّهِ وَكِتَابِهِ وَهْىَ لِي حَلاَلٌ " .
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."