Musannaf Ibn Abi Shayba 3:382

Abu Bakr narrated to us, he said: Hammad bin Khalid narrated to us, from Mu'awiyah bin Salih, from 'Iyad bin Abdullah al-Qurashi, he said: The Prophet, peace and blessings of Allah be upon him, saw a man prostrating on the fold of his turban. He gestured with his hand: "Raise your turban," and he pointed to his forehead.