Musannaf Ibn Abi Shayba 1:761

Ibn ‘Ulayyah narrated to us, from Ibn ‘Awn, who said: I said to al-Hasan or Mujahid, "How do you do with your feet during the ritual bath (ghusl) from major ritual impurity (janabah)?" He said, "As for me, I say like this." And Ibn ‘Awn described that he would pour water over the tops of his feet.