During the Plague of Hail, when Pharaoh asked Moses to pray that the plague come to an end, Moses responded,1 "When I leave the city I will spread my palms to G‑d, and the thunder will cease." The Midrash explains2 that he would not pray in the city because it was full of idols.3

Forbidden Symbols

We learn from this verse that it's forbidden to pray in a place that has idols.4 This prohibition includes icons that are worshipped, as well as crucifixes.

Many airports and hospitals have prayer rooms. If a cross is displayed in that room, a Jew should not pray there. Similarly, if one is in a hospital room which has a cross hanging on the wall, one should cover it, especially during prayer.5

One may not bow if a religious icon is in front of himIf one is praying in a private place (i.e., in a synagogue or home), he need not be concerned about religious symbols displayed elsewhere in the city, because he's in a separate area. If one has no choice but to pray in a room with religious icons, he should do so in a private corner.6 One may not bow if a religious icon is in front of him.7

A Physically Clean Environment

One may not pray, recite any blessings, or study Torah8 if urine or feces are visible within a range of four cubits. This prohibition is derived from the verse:9 "And you should… cover up your excrement, and your camp shall be holy"—meaning, when you are engaged in holy matters, all filth should be covered or removed.10

If urine or feces are in front of one, they must be far enough away not to be seen, and even if these items are outside of his range of vision, he must ensure that the stench of these items does not penetrate the four cubits surrounding him.11

If the feces and/or urine were produced by a child who is too young to consume grain food,12 one need not distance himself from them. Even if the child is older than this, if the urine and/or feces are in the child's diaper and the diaper is covered by the child's clothing or is in a bag, one may be within four cubits of the child (or bagged diaper), providing the odor is not sensed.13

One need not distance himself from animal feces; as long as the odor doesn't reach the person, he may pray nearby.14

An Environment Free of Lustful Desires

Since men can become aroused by the sight of a woman's body, it is forbidden for a man to pray in an area where even part of a woman's body is exposed, with the exception of the parts which may be exposed according to the dictates of modesty—i.e., the face, hands, and arms below the elbow. Some authorities maintain that a woman's lower leg, below the knee, may also be exposed,15 while others disagree.16 The restrictions on prayer only apply if the exposed area is the size of a handbreadth or larger.17

Because the main reason for this prohibition is to prevent lustful thoughts, the same rule applies to praying in the presence of an immodest picture, video, etc.18

One who is in a place where women are immodestly dressed should turn asideIn addition, the hair of a married woman must be covered. Some authorities argue that if a married woman doesn't normally cover her hair (although she should – see The Meaning of Hair Covering for more on this topic) a man may pray in her presence since the sight of her hair will not distract him,19 while others disagree.20

One who is in a place where women are immodestly dressed should turn aside so that the women are not in his line of sight. If this is impossible, he may pray with his eyes closed, or he should look down and avert his gaze.21

While a man may generally pray in the presence of a modestly dressed woman, a synagogue must have a separate area for men and women (see Separation in the Synagogue for more information and to understand the reason for this law).

A woman may pray in the presence of a man who is not fully clothed as long as his genitals are covered.22 The reason for this is that women are not as easily prone to lustful thoughts. If, in fact, a woman who is in the presence of a partially clothed man has lustful desires, she may not pray in his presence.23

A man may also not pray in the presence of exposed genitals, whether his own or another man's.24

Cleansing One's Body

The verse states:25 "Prepare yourselves to greet G‑d, O Israel." We learn from this that one should use the restroom before praying. It is considered disrespectful to stand in prayer before the King of kings when one has an accumulation of "filth" waiting to be expelled. Therefore, if one has any need to do so, he should make sure to relieve himself before beginning to pray.26 Even if this means he will miss praying with a minyan, one should take the time to relieve himself before praying.27 Preferably, one should arrange his schedule so that he does this before the time for prayer.28

If one prays with "filth" still in his body (i.e., after feeling the urge to expel it), his prayer is considered an abomination,29 and he must pray again after relieving himself. (This law only applies if his need to relieve himself was urgent. If, however, he would have been able to refrain from using the restroom for an hour and a quarter, his prayer is considered acceptable in retrospect.)

When one touches something dirty, he must wash his hands with water before prayingIf by the time one finishes using the bathroom the time of prayer will have passed (click here for more information), if he is able to refrain from going to the bathroom for one and a quarter hour, he should first pray. If he would be unable to do so, he should use the bathroom.30

All the above rules also apply to reciting blessings or studying Torah.31

Washing One's Hands

When one touches something dirty (e.g., shoes32) or a sweaty or dirty part of one's body, he must wash his hands with water before praying. This includes touching any part of the body which is normally covered, mucous from the nose or mouth, or scratching hair.33

If one does not have water readily available, and one is not sure whether or not he touched an unclean area, he may simply wipe his hands on the wall or a towel to clean them. If one is certain that he touched such an area, he should travel up to a kilometer in any direction to find water and wash his hands.34 If no water is available or if the time of prayer is passing, he should clean his hands with other items, as explained above.

The above law applies only to prayer; for Torah study, and the recital of other blessings, it is sufficient to clean one's hands on any item, and no water is needed.35

Appropriate Attire

Because when praying we stand before the King of kings, it is appropriate that we dress in a respectable manner. For this reason, one may not pray while bare-chested36 or barefoot (in a region that people do not go barefoot when meeting important people).37

It is forbidden for a man to pray or say any blessing while bareheaded.38 A married woman should also cover her head while praying.39 One should not pray while wearing shorts, even if he wears shorts routinely. The reason for this is because one would not meet an important person while wearing shorts.40 Similarly, one should not pray while wearing pajamas, as they are not considered respectable clothing.41

The Sages would only pray while wearing an upper garment (e.g., a jacket) in addition to their shirts.42 One who would normally meet an important person without putting on a jacket may pray without one, but it's praiseworthy to wear one anyway.43 The above applies to a hat as well.44

Because when praying we stand before the King of kings, it is appropriate that we dress in a respectable mannerIf a man is wearing only a robe, he must also wear underwear, or a belt over the robe, to separate between his heart and his genitals while praying.45 In addition, some authorities maintain that even if one is also wearing pants, which act as a separation, he should also put on a belt in order to mentally prepare himself to greet G‑d in an honorable manner.46

Donning a Gartel

It is customary amongst chassidim to wear a gartel ("prayer belt") during prayer, even if one is already wearing a belt on his pants.47 If one doesn't have a gartel, he should not miss prayer with a minyan in order to pray with a gartel.48

It is improper to use a tie or a piece of rope as a gartel, as one would not appear in front of a king while wearing these.49 Thus, if one doesn't have a gartel, he should pray without one. He may, however, use the above-mentioned substitutes under his jacket, where they are not visible.50

Please see Preparing for Prayer for more on this topic.