Musannaf Ibn Abi Shayba 1:1012

Al-Thaqafi narrated to us, from Ubayd Allah ibn Umar, from Nafi, that the wives of Abdullah ibn Umar and the mothers of his children used to menstruate. When they became pure, they would not wash the clothes they used to wear during their menstruation. And Ibn Umar used to say: "If you see blood, then wash it."