Chapter 12: The Book of The At-Tatbiq (Clasping One's Hands Together)
It was narrated that Mus' ab bin Sa' d said: "I prayed beside my father and I put my hands between my knees, and he told me: 'Put your hands on your knees.' Then I did that again and he struck my hands and said: 'We were forbidden to do that, and we were commanded to put our hands on our knees.'"
Sunan an-Nasa'i 1032