Musannaf Ibn Abi Shayba 1:991

Ibn Numayr narrated to us, from Zakariyya, from Firas, who said: I bought a young slave girl, and I would derive pleasure from her without having intercourse with her. So I asked al-Sha'bi, and he said: "As for you, perform ghusl (full ritual bath), and as for her, wudu (ablution) is sufficient for her."