Muwatta Malik Book 8, Hadith 28
Yahya related to me from Malik from Da'ud ibn al-Husayn that Ibn
Yarbu al-Makhzumi said, "I heard Zayd ibn Thabit say, 'The middle
prayer is the prayer of dhuhr.' "
Yahya related to me from Malik from Zayd ibn Aslam that Amr ibn Rafi said, "I was writing a Qur'an for Hafsa, umm al-muminin, and she said, 'When you reach this ayat, let me know, "Guard the prayers carefully and the middle prayer and stand obedient to Allah." When I reached it I told her and she dictated to me, 'Guard the prayers carefully and the middle prayer and the asr prayer and stand obedient to Allah.' "
Yahya related to me from Malik that he had heard that AIi ibn Abi Talib and Abdullah ibn Abbas used to say, "The middle prayer is the prayer of subh."
Malik said, "Out of all that I have heard about the matter, I prefer what Ali ibn Abi Talib and Abdullah ibn Abbas said."