Mishkat al-Masabih 832

Ibn ‘Abbas reported God’s Messenger as saying, “I have been commanded to prostrate myself on seven bones: the forehead, the hands, 1 the knees, and the extremities of the feet, 2 and not to fold back the clothing or the hair.” 1. i.e. the palms. 2. i.e. the toes. (Bukhari and Muslim.)