The 297th prohibition is that we are forbidden from not saving a Jew's life in a case where we see that his life is in danger and we have the ability to save him. For example, when someone is drowning in the sea and we can swim well to be able to save him; or a non-Jew wants to kill him and we are able to change his mind or to protect him from harm. [In such cases] there is a prohibition to refrain from saving him.

The source of this prohibition is G‑d's statement1 (exalted be He), "Do not stand still when your neighbor's life is in danger."

Our Sages say that even someone who denies that he has testimony is included in this prohibition, since he sees his brother's money being lost and is able to return it to him by testifying the truth. Another verse2 also refers to this: "and if he does not testify, he must bear his guilt." In the words of the Sifra: "What is the source of the law that when you can testify for someone, that you are forbidden from remaining silent? From the verse, 'Do not stand still when your neighbor's life is in danger.' What is the source of the law that if you see him drowning in the river, being attacked by robbers or by a wild animal that you are obligated to save him? From the verse, 'Do not stand still when your neighbor's life is in danger.' What is the source for the law that when a rodef is trying to kill someone, that you are obligated to save him even with the life [of the rodef]? From the verse, 'Do not stand still when your neighbor's life is in danger.' "

The details of this mitzvah are explained in tractate Sanhedrin.3