Sahih Ibn Khuzaymah

Hazrat Talhah bin Musa (may Allah have mercy on him) narrates from his esteemed father, he says that we used to pray in such a state that cattle would pass in front of us, so we asked the Prophet Muhammad (peace and blessings be upon him) about this issue, and he (peace be upon him) said: "(When) any one of you has a sutrah in front of him equal to the back part of a camel's saddle, then whatever passes in front of it will not harm him."

Sayyiduna Abu Dharr (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "When any one of you stands for prayer, if there is something in front of him equal to the back part of a camel's saddle, then that will serve as a sutrah (barrier) for him." Then the rest of the hadith was narrated. Bishr bin Mufaddal says that Yunus narrated to us a report exactly like the aforementioned hadith.

Ibn Jurayj (may Allah have mercy on him) says: I asked ‘Ata’ (may Allah have mercy on him), “The back wooden part of the camel-litter that has reached you, how much of it would suffice for it to be considered a sutrah?” He replied: “Equal to one handspan.”