Musannaf Ibn Abi Shayba 3:318

Ibn Fudayl narrated to us, from ‘Asim, from ‘Ikrimah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) passed by a person who was prostrating and was not placing his nose on the ground. He said: "Whoever performs a prayer in which the nose does not touch [the ground] as the forehead touches it, his prayer is not accepted."