Sunan an-Nasa'i, Hadith 3255 ⓘ
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.
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 .
also referenced under: Book 26, Hadith 60 (In-Book) & Volume 4, Book 26, Hadith 3257 (DarusSalam)