The Limbs Of Prostration And The Prohibition Of Tucking Up One's Hair And Garment Or Having Ones Hair In A Braid When Praying Sahih Muslim 491
Translation
It was narrated from Al-'Abbas bin 'Abdul Muttalib that he heard the Messenger of Allah (ﷺ) say
"When a person prostates, he prostates on seven part of the body: His face, his hands, his knees and his feet."