Musannaf Ibn Abi Shayba 3:4971

Abu Dawud narrated to us, from Shu'bah, from Ash'ath ibn Abi al-Sha'tha', who said: I went out with my father, 'Amr ibn Maymun, al-Aswad ibn Yazid, and Abu Wa'il. They used to pray two rak'ahs after the 'Asr prayer.