Sitting in Front of a Seated Worshipper

Is it permissible to sit in front of someone praying who is not standing, such as on a bus, or in front of an elderly or sick person?

It is forbidden to sit in front of him and to the sides of the worshipper, and according to the Rema even behind him, because it appears as if one is not accepting the yoke of the kingdom of heaven, even if the worshipper himself is praying while seated. On a bus, it is permitted as will be explained.

This rule is permitted in 4 cases.

1. If one is engaged in prayer, and in the Mishnah Berurah it is lenient even when engaged in Torah study, in a pressing situation, and behind him even not in a pressing situation.

2. If the person sitting is weak and it is evident that he is sitting due to his weakness.

3. When there is a permanent partition 10 tefachim high and 4 tefachim wide.

4. When the person sitting was already seated and another came into his boundary and began to pray, and this permission does not apply to prayer in the synagogue as it is a place of prayer and is not considered entering his boundary.

Therefore, in front of a person sitting on a bus and praying, if he sat before the other arrived, he does not need to stand up, since the worshipper entered his boundary and it is not a place designated for prayer.

Gemara, Tractate Berachot, page 31: "I am the woman standing here with you," said Rabbi Yehoshua ben Levi: from here, it is forbidden to sit within four cubits of a prayer. And so it is ruled in Shulchan Aruch, Orach Chaim, Siman 102, Paragraph 1: "It is forbidden to sit within four cubits of a worshipper; both in front and to the sides, and the Rema added that it is forbidden even behind."

And it is written in Ketzot HaShulchan, Siman 20, that it is forbidden to sit even within four cubits of a seated worshipper.