Man and Woman’s Washing from Single Vessel

Ibn ‘Abbaas (radhiAllaahu ‘anhumaa) narrates that

One of the wives of the Prophet (sallallaahu ‘alaihi wa sallam) took a ghusl from Janaabah then saw Rasoolullah (sallallaahu ‘alaihi wa sallam) about to take a ghusl from the water remaining – so she informed him that she had made ghusl therefrom – so Rasoolulah said Nothing makes the water impure.

[Reported by Abu Dawood (no.67), and an-Nasaa’ee (no.326), 
and at-Tirmidhee who declared it to be hasan saheeh, 
and Ibn Maajah (no.370)].

Ibn ‘Abd ul-Barr says:

There is nothing in the Sharee’ah to prevent each of them washing with the water remaining from the other – either together or one after the other, and this is the saying of the scholars of the different lands and the great majority of scholars – and the ahaadeeth about it are Mutawaatir.

(Al-Istidhkaar, 1/373).