Musnad Abu Ya'la al-Mawsili 109:177

Muhammad ibn Isma'il ibn Abi Samina narrated to us, Mubashir ibn Isma'il narrated to us, Abu Bakr al-Ghassani narrated to us, from Hakim ibn Umayr, from Jabir: That the Prophet, may Allah bless him and grant him peace, used to prostrate on the upper part of his forehead, along with the hairline.