Musannaf Ibn Abi Shayba 3:4962

Waki' narrated to us, he said: Sufyan narrated to us, from Abu Ishaq, from 'Asim ibn Damrah, from 'Ali, he said: The Prophet, may Allah bless him and grant him peace, used to pray two rak'ahs after every obligatory prayer, except for the Fajr and the 'Asr.