Musnad Abu Ya'la al-Mawsili 217:22

Abu Khaythama narrated to us, Sa'id ibn Sulayman narrated to us, 'Abbad narrated to us, from Hanzala al-Sadusi, who said: I heard 'Abdullah ibn al-Harith ibn Nawfal say: Maymuna bint al-Harith, the wife of the Prophet (may Allah bless him and grant him peace), narrated to me that the Prophet (may Allah bless him and grant him peace) used to pray two rak'ahs before the 'Asr prayer.