A Person passing directly in front of a Worshipper in Prayer does not invalidate His Prayer

Question :

If a person prays and another person passes in front of him, is his prayer invalidated and must he repeat it?

Answer:

A person passing directly in front of a worshipper in prayer does not invalidate his prayer; only three things invalidate it, according to the most correct saying of the scholars: An adult woman, a black dog, as opposed to dogs of other colors, and a donkey. Thus it was reported from the Prophet that he said:
"A Muslim man's prayer is cut off, if he does not have in front of him something such as a camel saddle, by a woman, a donkey and a black dog.

It was said: "O Messenger of Allah! Why the black dog, as opposed to the red one or the yellow one?" He said:
*The black dog is a devil.

The meaning is that these three things cut off the prayer, according to the most authoritative opinion of the scholars. But the passing of any other person invalidates his reward, so he should be prevented by the worshipper from passing in front of him, if it is possible; and it is not permitted for anyone to pass in front of a worshipper in prayer, because the Prophet forbade it, saying:
if the one who passes in front of a worshipper in prayer knew the sin he was committing, he would wait for forty (years), and that would be better for him than passing in front of the worshipper in prayer.

And he ordered whoever prayed towards a Sutrah not to let people pass in front of him, but to prevent them; he said:

If any of you prayed towards something which screens him from the people (a Sutrah), and someone wished to pass before him, he should stop him, but if he refuses (to stop trying to pass), then he should fight him, for he is a devil.

So the Sunnah proves that the worshipper should repel the one who tries to pass in front of him, even if he is not one of the aforementioned three, and whether it be a human being or an animal - if he is able to do so. However, if he defeated the worshipper's efforts and passed in front of him, it would not harm his prayer.

It is a part of the Sunnah for the Muslim to place something in front of him, be it a chair, a spear he sticks in the ground, a wall or one of the pillars in the mosque. Then if people pass behind the Sutrah, it will not harm his prayer; but their passing between him and his Sutrah is what is forbidden.

If the one passing in front of the worshipper was a woman, a donkey or a black dog, his prayer would be cut off. Likewise, if these three passed close in front of him while he did not have a Sutrah, closer than three cubits or less, it would cut off his prayer. However, if they passed far from him, at a distance of more than three cubits, then it would not harm his prayer. This is because the Prophet prayed in the Ka'bah and he placed three cubits between him and the west wall, so the scholars cite this as proof that this is the distance of the Sutrah. And the meaning of "cutting off" is invalidation. The majority say that this means that the prayer is not perfect, but the correct view is that it invalidates the prayer and necessitates its repetition. And through Allah is attained success.