Hadith: We used to pray and animals would pass in front of us. We mentioned that to the Messenger of Allah (may Allah's peace and blessings be upon him) so he said: If anything, like the back of the saddle, is placed in front of anyone of you, then nothing that passes in front of him (but behind that thing) can harm him

عن طلحة بن عبيد الله رضي الله عنه قال: كنَّا نصلِّي والدواب تمرُّ بين أيدينا فذكرنا ذلك لرسول الله صلى الله عليه وسلم فقال: «مِثْلُ مُؤْخِرَةِ الرَّحْلِ تكون بين يدي أحدكم، ثم لا يضُرُّه ما مر بين يديه».
[صحيح] - [رواه مسلم]

Talhah ibn ‘Ubaydullāh (may Allah be pleased with him) reported: We used to pray and animals would pass in front of us. We mentioned that to the Messenger of Allah (may Allah's peace and blessings be upon him) so he said: "If anything, like the back of the saddle, is placed in front of anyone of you, then nothing that passes in front of him (but behind that thing) can harm him."
[Authentic hadith] - [Narrated by Muslim]

Explanation

Talhah ibn ‘Ubaydullāh (may Allah be pleased with him) informs us that they used to pray and that animals would pass in front of them. They mentioned that to the Messenger of Allah (may Allah's peace and blessings be upon him) so he told them that as long as there is something between the praying person and the passer-by, like the end of a saddle, then his passing will not harm him. Some of the benefits of the Sutrah are: maintaining the prayer, staying away from things that reduce its reward, repelling any guilt from the passer-by, and sparing him any difficulty or embarrassment.