Musannaf Ibn Abi Shayba 3:3595

Abu Mu'awiyah narrated to us, from al-A'mash, from 'Amr ibn Murrah, from Abu 'Ubaydah, who said: The prayer of 'Abdullah [ibn Mas'ud] which he would not abandon was four [rak'ahs] before Dhuhr, and two [rak'ahs] after it, and two [rak'ahs] after Maghrib, and two [rak'ahs] after 'Isha, and two [rak'ahs] before Fajr.