Musannaf Ibn Abi Shayba 3:189

Abu Bakr narrated to us, he said: Hatim ibn Isma'il narrated to us, from Ja'far, from his father, he said: The woodcutters came to the Prophet, may God bless him and grant him peace, and they said: "O Messenger of God, we are always traveling, so how should we perform the prayer?" He said: "Glorify [God] with three glorifications in bowing, and three glorifications in prostration."