Musannaf Ibn Abi Shayba 3:1565

Yazid ibn Harun narrated to us, he said: Al-Hajjaj ibn Hassan informed us, he said: I heard Abu Mijlaz, or I asked him, he said: I said, "How should one do it?" He said: "He places the palm of his right hand upon the back of his left hand, and he places them below the navel."