Musannaf Ibn Abi Shayba 3:6357

Waki’ narrated to us, he said: Nafi’ ibn ‘Umar al-Jumahi narrated to us, from Ibn Abi Mulaykah, from one of the wives of the Prophet (may Allah bless him and grant him peace), that she was asked about the recitation of the Prophet (may Allah bless him and grant him peace). She said: "You would not be able to do it." It was said to her: "Inform us of it." So she recited a recitation in which she slowed down.