Yahya related to me from Malik from Zayd ibn Aslam that Amr ibnRafi said, "I was writing a Qur'an for Hafsa, umm al-muminin, and shesaid, 'When you reach this ayat, let me know, "Guard the prayerscarefully and the middle prayer and stand obedient to Allah." When Ireached it I told her and she dictated to me, 'Guard the prayerscarefully and the middle prayer and the asr prayer and stand obedientto Allah.' "
App reference: Book 8, Hadith 27
USC-MSA web (English) reference: Book 8, Hadith 27
Arabic reference: Book 8, Hadith 316