كتاب الحيض
3  
The Book of Menstruation
(10)
Chapter: The amount of water with which it is recommended to perform ghusl in the case of janabah; a man and woman washing from a single vessel; one of them washing with the left-over water of the other
(10)
باب الْقَدْرِ الْمُسْتَحَبِّ مِنَ الْمَاءِ فِي غُسْلِ الْجَنَابَةِ وَغُسْلِ الرَّجُلِ وَالْمَرْأَةِ فِي إِنَاءٍ وَاحِدٍ فِي حَالَةٍ وَاحِدَةٍ وَغُسْلِ أَحَدِهِمَا بِفَضْلِ الآخَرِ
Sahih Muslim 321 b

Hafsa, daughter of 'Abd al-Rahman b. Abu Bakr, reported that 'A'isha narrated to her that she and the Messenger of Allah (ﷺ) took a bath from the same vessel which contained water equal to three Mudds or thereabout.

وَحَدَّثَنِي مُحَمَّدُ بْنُ رَافِعٍ، حَدَّثَنَا شَبَابَةُ، حَدَّثَنَا لَيْثٌ، عَنْ يَزِيدَ، عَنْ عِرَاكٍ، عَنْ حَفْصَةَ بِنْتِ عَبْدِ الرَّحْمَنِ بْنِ أَبِي بَكْرٍ، - وَكَانَتْ تَحْتَ الْمُنْذِرِ بْنِ الزُّبَيْرِ - أَنَّ عَائِشَةَ، أَخْبَرَتْهَا أَنَّهَا، كَانَتْ تَغْتَسِلُ هِيَ وَالنَّبِيُّ صلى الله عليه وسلم فِي إِنَاءٍ وَاحِدٍ يَسَعُ ثَلاَثَةَ أَمْدَادٍ أَوْ قَرِيبًا مِنْ ذَلِكَ ‏.‏
Reference : Sahih Muslim 321b
In-book reference : Book 3, Hadith 52
USC-MSA web (English) reference : Book 3, Hadith 628
  (deprecated numbering scheme)