Musannaf Ibn Abi Shayba 3:4831

Ibn ‘Uyaynah narrated to us, from Ibn Abi Najih, from ‘Ata’, Tawus, and Mujahid, who said: If she becomes pure before the setting of the sun, she prays Dhuhr and ‘Asr. And if she becomes pure before the rising of the dawn, she prays Maghrib and ‘Isha’.