Musannaf Ibn Abi Shayba 3:200

Abu Bakr narrated to us, he said: Hafs narrated to us, from al-Ja‘d, a man from the people of Medina, from a daughter of Sa‘d: That she used to exaggerate in bowing, lowering [her head] while saying "Allahu Akbar." So Sa‘d said to her: "It is sufficient for you when you place your hands upon your knees."