Musannaf Ibn Abi Shayba 1:1011

Ghundar narrated to us, from Ash'ath, from al-Hasan, from his mother, from Umm Salamah, that a woman asked her about a menstruating woman wearing a garment to pray in it. Umm Salamah said: "If there is blood on it, she should wash the place of the blood; otherwise, she may pray in it."