Musannaf Ibn Abi Shayba 3:4828

Abu Bakr narrated to us, he said: Hatim ibn Isma'il narrated to us, from Muhammad ibn 'Uthman al-Makhzumi, he said: My grandmother informed me, from a freed slave of 'Abd al-Rahman ibn 'Awf, he said: I heard him saying: "If the menstruating woman becomes pure before the setting of the sun, she prays the Dhuhr and the 'Asr. And if she becomes pure before the dawn, she prays the Maghrib and the 'Isha'."