مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2785
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 following janabah. Then the Prophet (ﷺ) came and did ghusl with her left over water. She said: I did ghusl from it. The Messenger of Allah (ﷺ) said: "Nothing makes water najis (impure)."
Musnad Ahmad 2805Saheeh because of corroborating evidence]