Sunan an-Nasa'i, hadith 3255

أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ أَنْبَأَنَا أَبُو مُعَاوِيَةَ، قَالَ حَدَّثَنَا هِشَامُ بْنُ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم تَزَوَّجَهَا وَهِيَ بِنْتُ سِتٍّ وَبَنَى بِهَا وَهِيَ بِنْتُ تِسْعٍ ‏.‏

It was narrated from 'Aishah that the Messenger of Allah married her when she was six years old, and consummated the marriage with her when she was nine