Sahih al-Bukhari 4951
In-book no 4951حَدَّثَنَا 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.
Narrated 'Urwa: 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).