Musannaf Ibn Abi Shayba 1:895

Yahya ibn Sa'id narrated to us, from al-Ja'd, from 'A'ishah bint Sa'd, who said: Sa'd used to command his slave girl to bring him the water for purification from the jar, and she would dip her hand into it. It would be said: "She is menstruating." He would say: "Her menstruation is not in her hand."