Musannaf Ibn Abi Shayba 3:5041

Ibn Numayr narrated to us, from Ubayd Allah ibn Umar, from Nafi, from Ibn Umar, that he used to say to his slave girl: "Hand me the prayer mat (khumra) from the mosque." She would say: "I am menstruating." He would say: "Indeed, your menstruation is not in your hand."