Musnad Abu Ya'la al-Mawsili 150:341

Ubayd Allah ibn Umar al-Qawariri narrated to us, Yazid ibn Zuray' narrated to us, Khalid al-Hadhdha' narrated to us, from Ibn Shaqiq—and he is Abdullah—who said: I asked Aisha about the prayer of the Messenger of Allah, may Allah bless him and grant him peace. She said: He used to pray four [rak'ahs] before the Dhuhr, then he would go out and pray the Dhuhr, then he would return and pray two rak'ahs. Then he would go out for the Maghrib, then he would return and pray two rak'ahs. Then he would go out for the Isha, then he would return and pray two rak'ahs.