سنن ابن ماجه

It was narrated from Musa bin Talhah that his father said: “We used to perform prayer while the beasts were passing in front of us. That was mentioned to the Messenger of Allah (ﷺ) and he said: ‘If something like the hand of a saddle* is placed in front of anyone of you, it will not matter whoever passes in front of him.”

* It is the piece of wood on the camel saddle which is held on to (to climb onto the camel).