Imam Malik's Muwatta, Chapter: Prayer in Congregation

Yahya related to me from Malik from Zayd ibn Aslam from al-Qaqa ibn Hakim that Abu Yunus, the mawla of A'isha, umm al-muminin said, ''A'isha ordered me to write out a Qur'an for her. 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.' A'isha said, 'I heard it from the Messenger of Allah, may Allah bless him and grant him peace.' "