Musnad Ahmad 5:650

Abdullah narrated to us, Abu Khaythama narrated to me, Jarir and Muhammad ibn Fudayl narrated to us, from Mutarrif, from Abu Ishaq, from Asim ibn Damrah, from Ali, who said: "The Prophet, peace and blessings of Allah be upon him, would not perform a prayer except that he performed two rak'ahs after it."