مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3096
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn ‘Abbas (رضي الله عنه) said: The Prophet (ﷺ) and Maimoonah became junub, and Maimoonah did ghusl in a tub, and left some water. The Prophet (ﷺ) wanted to do ghusl with it and she said: O Messenger of Allah, I did ghusl with it. He - meaning the Prophet (ﷺ) - said: "Water does not become junub." Or he said: "Water does not become najis."
Musnad Ahmad 3120Saheeh because of corroborating evidence; this is a da’eef i