مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2099
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn 'Abbas (رضي الله عنه) that one of the wives of the Prophet (ﷺ) did ghusl for janabah and the Prophet (ﷺ) did ghusl or wudoo’ with her left-over water.
Musnad Ahmad 2101Saheeh because of corroborating evidence]