مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3357
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn ‘Abbas (رضي الله عنه) that The Messenger of Allah (ﷺ) came out of the outhouse and food was brought to him and water for wudoo’ was offered to him, but he said: "I have only been commanded to do wudoo' when I get up to pray.”
Musnad Ahmad 3381Hs isnad is saheeh, Muslim (374)]