Musnad Abu Ya'la al-Mawsili 245:7

Ubayd Allah ibn Mu'adh al-'Anbari narrated to us, my father narrated to us, from Shu'bah, from Abu al-Tayyah, who said: I heard Humran ibn Aban saying: Mu'awiyah ibn Abi Sufyan delivered a sermon to us and said: "Indeed, you perform a prayer that the Messenger of Allah (peace and blessings of Allah be upon him) did not use to perform, and he used to forbid it." He meant the two rak'ahs after the 'Asr prayer.