Musnad Abu Ya'la al-Mawsili 245:32

'Amr ibn Muhammad narrated to us, 'Ala' ibn Hilal al-Raqqi narrated to us, 'Ubayd Allah ibn 'Amr narrated to us, from Zayd ibn Abi Unaysah, from Abu al-Fayd, from Mu'awiyah ibn 'Ali al-Sulami, who said: Mu'awiyah ibn Abi Sufyan led us in the Maghrib prayer, [praying] three [rak'ahs]. He stood up during the two rak'ahs, so they glorified Allah (said "Subhan Allah") to him. He gestured to them to stand. When he finished his prayer and performed the taslim, he turned and addressed them, then said: "I saw the Messenger of Allah (may Allah bless him and grant him peace) do as you saw me do. And were it not that I saw him do it, I would not have done it."