The 289th prohibition is that we are forbidden from killing each other.

The source of this prohibition is G‑d's statement1 (exalted be He), "Do not commit murder."

The punishment for violating this prohibition is execution by decapitation. [The death penalty is derived] from G‑d's statement2 (exalted be He), "You must even take him from My altar to put him to death."

The details of this mitzvah are explained in the 9th chapter of tractate Sanhedrin3 and the 2nd chapter of Makkos.