Musannaf Ibn Abi Shayba 3:4833

Hafs ibn Ghiyath narrated to us, from Hajjaj, from Abu Ma'shar, from Ibrahim, who said: If a menstruating woman becomes pure at the end of the day, she performs the Dhuhr and Asr prayers. And if she becomes pure at the end of the night, she performs the Maghrib and Isha prayers.