Musnad Ahmad 6:8

'Umar ibn 'Ubayd narrated to us, Simak ibn Harb narrated to us, from Musa ibn Talhah, from his father, who said: We used to pray while the animals would pass in front of us. We mentioned that to the Prophet, peace and blessings of Allah be upon him, and he said: "Like the back part of a saddle being in front of one of you, then it does not harm him what passes in front of him." And 'Umar said once: "In front of him."