Musnad Ahmad 435:106

Rawh narrated to us, he said: Abu Umayyah ‘Amr ibn Yahya ibn Sa‘id narrated to us, he said: I heard my grandfather narrating that Mu‘awiyah took the water container after Abu Hurayrah, following the Messenger of Allah (may Allah bless him and grant him peace) with it, and Abu Hurayrah was complaining of an ailment. While he was performing ablution for the Messenger of Allah (may Allah bless him and grant him peace), he raised his head toward him once or twice while he was performing ablution, and he said: "O Mu‘awiyah, if you are put in charge of an affair, then fear Allah, the Almighty and Majestic, and be just." He said: I continued to think that I would be tested with authority due to the statement of the Prophet (may Allah bless him and grant him peace), until I was tested.