Musannaf Ibn Abi Shayba 3:467

Abu Bakr narrated to us, he said: Abu al-Ahwas Salam ibn Sulaym narrated to us, from Simak ibn Harb, from Musa ibn Talhah, from his father, who said: The Prophet (peace and blessings of Allah be upon him) said: "If one of you places in front of him, while he intends to pray, something like the back of a saddle, then let him pray, and let him not care who passes behind that."