Pikuach nefesh

In the event that a person is in critical danger, most mitzvot become inapplicable if they would hinder the ability to save oneself or someone else.

In the Talmud (Yoma 85b), Samuel of Nehardea interpreted the verses above to imply, "Live by them [God's statutes and laws], and do not die by them".

The Talmud discusses a number of cases as examples in which biblically mandated laws can be disregarded for the sake of saving a human life.

[4] The Mishna discusses when one is permitted to break one's fast on Yom Kippur: "If one is seized by a ravenous hunger, he may be given to eat even unclean things until his eyes are lightened."

For example, if a person is feeling "extreme pain", this may be tremendously uncomfortable, but it is unclear whether it may lead to death.

It is always considered preferable to err on the side of caution (i.e., "violating" Jewish laws), even if this later turns out to be unnecessary.

[12] According to some halakhic rulers, organ donation in Jewish law is one classic example of the obligation to violate a commandment because of pikuach nefesh.

The earliest known example of this took place in 167 BCE, when Mattathias and the Hasmoneans declared that it was permitted for their followers to fight on the Sabbath day to defend themselves from attack.

One is allowed to travel in order to save another's life, and medical care may be provided to critically ill patients (see Driving on Shabbat).

According to Moshe Feinstein, it is permissible to travel to accompany a woman in labor to a hospital because the Talmud is especially solicitous of health with respect to pregnancy and childbirth.

[21] If a medical emergency is known or suspected that warrants placing a phone call rather than transportation in a motor vehicle, the telephone may be used.

If the situation has a lower level of urgency, the receiver shall be removed and the buttons pressed in shinuy, or an unusual manner (e.g., by using the elbow or the knuckles, or a pencil).

In the Babylonian Talmud, Chapter 82a of Tractate Yoma mentions pregnancy cravings for non-kosher food (the passage discusses a pregnant woman who craves pork on Yom Kippur) as the paradigmatic example of a presumed life-threatening situation where a person is allowed to eat non-kosher food (and is permitted to eat it on Yom Kippur).

Fasting, as much as possible, takes priority over prayer (and thus more should not be eaten merely to enable one to attend synagogue or pray with more concentration).

[5] A person who becomes severely dehydrated during any fast shall consume sufficient fluids to restore their body to normal hydration levels.

[26] A famous example of this is found in the Talmudic rendition of Hannah and her seven sons, which states that the family was martyred to avoid worshiping idols.

[27] Despite the heavy prohibition, Rabbinical commentary makes exceptions for Jews forced to abandon Judaism or raised without sufficient knowledge of it.

The "rodef" assertion is also used to permit the separation of conjoined twins when it is likely or even certain that one will die as a result of the operation if this is necessary to save the other.

[31] A ZAKA delegation, a rescue team made up of Haredi men, worked in the Haitian capital of Port-au-Prince soon after the 2010 Haiti earthquake.

For example, while many mainstream Orthodox authorities agreed that avoiding the risk of disease was worth missing an in-person service, communities of Haredi and Hasidic Jews continued to gather in synagogue.