Musannaf Ibn Abi Shayba 1:868

868. Humayd ibn Abd al-Rahman narrated to us, from Dinar, who said: I said to al-Hasan, "The non-Arab slave girl does not know how to perform ghusl (ritual bath)." He said: "Command her to wipe her private part with a cloth, and to wash it with water, inside and out. Then let her perform her wudu (ablution) for prayer, and then perform ghusl."