Musannaf Ibn Abi Shayba 3:194

Abu Bakr narrated to us, he said: Kathir ibn Hisham narrated to us, from Ja'far ibn Burqan, who said: I asked Maymun about the extent of the bowing (ruku') and the prostration (sujud). He said: "I do not consider it to be less than three glorifications (tasbihat)." Ja'far said: So I asked al-Zuhri, and he said: "When the bones fall into place and settle." I said to him: "Maymun says three glorifications." He said: "That is what I am telling you, something similar to that."