Musannaf Ibn Abi Shayba 21:579

Mu'awiyah narrated to us, from Hajjaj, from al-Hakam, from 'Abd al-Rahman ibn Yazid, from 'Abdullah, who said: Two things are an innovation: that a man stands after he finishes his prayer, facing the Qiblah, supplicating. And that he performs the second prostration, then considers it a duty upon him to press his buttocks to the ground before he rises.