Yahya related to me from Malik from Zayd ibn Aslam that Amr ibn
Rafi said, "I was writing a Quran 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.' "
Muwatta Malik Book 8, Hadith 27