Musannaf Ibn Abi Shayba 3:1104

Abu Bakr narrated to us, he said: Zayd ibn al-Hasan narrated to us, he said: ‘Abd al-Malik ibn al-Rabi‘ ibn Sabrah ibn Ma‘bad al-Juhani narrated to me, he said: My father narrated to me, from my grandfather, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "When the boy reaches seven years, command him to pray. And when he reaches ten, strike him for it."