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 322

Ibn Abbas said:

Maimuna (the wife of the Holy Prophet) reported to me that she and the Messenger of Allah (ﷺ) took a bath from one vessel.
وَحَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، وَأَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ جَمِيعًا عَنِ ابْنِ عُيَيْنَةَ، قَالَ قُتَيْبَةُ حَدَّثَنَا سُفْيَانُ، عَنْ عَمْرٍو، عَنْ أَبِي الشَّعْثَاءِ، عَنِ ابْنِ عَبَّاسٍ، قَالَ أَخْبَرَتْنِي مَيْمُونَةُ، أَنَّهَا كَانَتْ تَغْتَسِلُ هِيَ وَالنَّبِيُّ صلى الله عليه وسلم فِي إِنَاءٍ وَاحِدٍ ‏.‏
Reference : Sahih Muslim 322
In-book reference : Book 3, Hadith 55
USC-MSA web (English) reference : Book 3, Hadith 631
  (deprecated numbering scheme)