Sahih al-Bukhari 5158
Sahih al-Bukhari · Book 67: Wedlock, Marriage (Nikaah) · Whoever consummated his marriage with a lady of nine years of age
Narrated 'Urwa:
حَدَّثَنَا قَبِيصَةُ بْنُ عُقْبَةَ ، حَدَّثَنَا سُفْيَانُ ، عَنْ هِشَامِ بْنِ عُرْوَةَ ، عَنْ عُرْوَةَ ، تَزَوَّجَ النَّبِيُّ صلى الله عليه وسلم عَائِشَةَ وَهْىَ ابْنَةُ سِتٍّ وَبَنَى بِهَا وَهْىَ ابْنَةُ تِسْعٍ وَمَكَثَتْ عِنْدَهُ تِسْعًا.
The Prophet (ﷺ) wrote the (marriage contract) with `Aisha while she was six years old and consummated his marriage with her while she was nine years old and she remained with him for nine years (i.e. till his death).