Being Careful With Other People's Money

One who steals something from another person, violates a Torah prohibition. The Torah prohibits multiple forms of taking something that really belongs to another:

1. גניבה - geneva is to take something from someone else's possession without their knowledge.
2. גזילה - gezela is grabbing something from someone else's possession by force, in plain sight
3. עושק - oshek is to withhold somebody else' item from them with force, such as they gave you money and now are asking for it back and you refuse to give it.
4. Additionally, Baba Metzia 61a-b points out that ribbit (lending with interest), [Onaat Mamon] (overcharging), and imbalanced weights are also forms of stealing. see Rashi there d"h Lama Li that these are also forms of causing financial loss to another person
5. One who commits fraud, both seller to buyer and buyer to seller, violates a Torah prohibition.

Statements of Chazal Regarding the Severity

1. Rav Yehudah in Bava Basra (165a) informs us that most people steal, a minority engage in illicit sexual activity, and everyone says Avak Loshon Hara. The Rishonim explain that the Gemara is not referring to outright stealing such as shoplifting but more subtle forms of stealing that afflict our interactions as buyers, employers, landlords, etc. A person who keeps stolen money is both subject to severe punishments for stealing and also sets himself up to one day become a victim. Thus, it is incumbent upon everyone to be aware of the Halachos of other people's money.

Possible Exceptions

1. Even if one takes an item from his friend to benefit his friend it is prohibited. For instance, one cannot take an old garment from his friend with the intention of buying him a new one. One cannot also take away something from someone to teach him a lesson. The one exception to this rule is a teacher who is able to confiscate an item to discipline the class. While the teacher should return the item, if the teacher feels that discipline will only be achieved with the destruction of the item he may do so.
2. One cannot even take someone else's item to avoid a sickness or pain even if he intends to repay in full. If the situation is life-threatening one may steal but must pay back afterwards. Chazal also permit using someone else's item to prevent a sudden lost. For instance, if one's bottle of whiskey suddenly cracked one may one use someone else's utensil to catch the whiskey before it all leaks out. This is only on the condition that he will pay the owner afterward if the owner lost money such as if one poured out soda or milk from the other person’s vessel to save the whiskey.
3. If a candyman was giving out lollipops to little children and one child aggressively took many lollipops at the expense of another child, the father cannot grab a lollipop from the aggressive kid and give it to his own son. This only applies if the person giving out lollipops did not care who gets and how many, and thus gave the lollypop for the aggressive child. However, if the candyman wanted everyone to get equally, then the child who took too many lollipops is a thief, and one can take a lollypop away from him.
4. Stealing equally applies to an institution such as a shul or Yeshiva. For instance, if Yeshiva guys are really hungry and want to break into the Yeshiva kitchen to have a snack, they would be stealing. The management of the intuition is empowered by the donors to decide how the institution’s assets are to be used. They are like treasurers of the Beis Hamikdash in this case and have the authority to decide how and when to give to others.

Stealing Less than a Prutah

1. Stealing is prohibited even if it's less than a Prutah, which is a few cents. However, if nobody would object to taking such an item it is not considering stealing. Nonetheless, it is preferable not to take such an item without permission.

Stealing as a Joke

1. Stealing is prohibited even if one is taking a friend's possession as a practical joke or to annoy him, even if he has every intention of returning the item after the joke has run its course.

Stealing from a Non-Jew

1. It is absolutely forbidden to steal from a non-Jew.

Borrowing Without Permission

The gemara records a story in which the sharecropper of Mari Bar Isak took fruit to some of Amoraim while Mari Bar Isak was away. Some of the Amoraim ate the fruits, while Rav Ashi did not. Rashi explains that Rav Ashi was concerned that the sharecropper was taking Mari Bar Isak’s fruit without permission and didn’t want to benefit from stolen goods. If so, what were the other Amoraim thinking? Tosfot (Bava Metsia 22a s.v. mar) explains that they assumed that the sharecropper was giving his own fruits. Then Tosfot adds that it would not have been a correct justification if the other Amoraim assumed that the sharecropper took Mari’s fruits, but once Mari would find out about it, he would be okay with it. Tosfot proves that an expression of intent isn’t effective for past events from the topic of yeush shelo medaat, assuming someone would relinquish ownership if an item is lost.

Tosfot’s opinion is quoted by the Shulchan Aruch and accordingly it would be prohibited to take someone else’s property even if one assumes that they would be agreeable when he finds out. Even though the Shach (C.M. 358) disagrees, the poskim (Kitzur Shulchan Aruch 182:13, Aruch HaShulchan 358:8) follow the opinion of Tosfot. Nonetheless, Rabbi Bodner (Halachos Of Other People’s Money p. 26) quotes poskim who say that if a friend or relative have allowed you to take a particular item in the past with regularity it would permitted to take it without consent.

Stealing Sleep

In a number of teshuvot, Rav Menashe Klein in Mishneh Halachot (12:443-4, 14:199-200) discusses the question of whether waking someone up is really considered stealing. On the one hand, he tries to show that the prohibition of stealing even applies to non-tangible items that one wouldn’t have to return. For example, the Tosefta (Bava Kama 3:7) says that it is considered stealing to trick someone (genivat daat). Rav Klein explains that the root of stealing is causing someone anguish and doesn’t only apply to tangible items. Similarly, waking someone up causes that person discomfort and could be considered stealing.

On the other hand, he writes that the Mishna (B”B 20b) speaks of people having the legitimate right to complain that their neighbors make too much noise with their guests and prevent them from sleeping. The Meiri on that Mishna describes such an action as intangible damage and not stealing. Based on the Meiri, the Mishneh Halachot prefers to say that waking someone up is an issue of damage and not stealing. Regarding a waking up someone who is sick and needs his sleep, certainly waking them up is forbidden just like damaging them physically. Lastly, Rav Klein writes that wasting someone’s time in it of itself is stealing because time is the most valuable thing a person has.
Ten Minute Halacha - Gezel Sheina Stealing Sleep by Rabbi Aryeh Lebowitz

Benefiting from Stolen Goods

1. It is forbidden to buy something that a thief stole, whether the thief is Jewish or non-Jewish.

Laws for a Store Owner

1. One may not mix good and bad fruit together in order to sell the bad fruit at the price of the good fruit. However, one may mix two types of fruits even though one may be less preferable to his fellow as long as it is recognizable.