It was narrated from Abu Bakr bin Hafs: "I heard Abu Salamah say: 'I entered upon 'Aishah and her foster-brother was with her. He asked her about the Ghusl of the Prophet (ﷺ). She called for a vessel in which was a Sa' of water, then she concealed herself and performed Ghusl and poured water over her head three times.'"
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ أَبِي بَكْرِ بْنِ حَفْصٍ، سَمِعْتُ أَبَا سَلَمَةَ، يَقُولُ دَخَلْتُ عَلَى عَائِشَةَ - رضى الله عنها - وَأَخُوهَا مِنَ الرَّضَاعَةِ فَسَأَلَهَا عَنْ غُسْلِ النَّبِيِّ صلى الله عليه وسلم فَدَعَتْ بِإِنَاءٍ فِيهِ مَاءٌ قَدْرَ صَاعٍ وَسَتَرَتْ سِتْرًا فَاغْتَسَلَتْ فَأَفْرَغَتْ عَلَى رَأْسِهَا ثَلاَثًا .
sunnah.com