Musnad Abu Ya'la al-Mawsili 161:45

Mus'ab ibn 'Abd Allah narrated to us, he said: Ibn al-Darawardi and Ibn Abi Hazim narrated to me, from Yazid ibn al-Had, from Muhammad ibn Ibrahim, from 'Amir ibn Sa'd, from al-'Abbas ibn 'Abd al-Muttalib, that he heard the Prophet, peace and blessings of Allah be upon him, saying: "When the servant prostrates, seven limbs prostrate with him: his face, his two palms, his two knees, and his two feet."