Musannaf Ibn Abi Shayba 3:288

Abu Bakr narrated to us, he said: Hafs narrated to us, from al-Hajjaj, from Abu Ishaq, from al-Bara’, he said: He was asked: "Where did the Prophet, may Allah bless him and grant him peace, place his face?" He said: "He used to place it between his palms," or he said: "his hands," meaning in prostration.