Musannaf Ibn Abi Shayba 3:193

Abu Bakr narrated to us, he said: Abdullah bin Ajlah narrated to us, from al-Hasan bin Ubayd Allah, he said: al-Musayyab bin Rafi’ asked Ibrahim and said: "How many [tasbihs] suffice a man when he places his head in prostration?" Ibrahim said: "Three tasbihs."