The 296th prohibition is that we are forbidden from taking ransom money to spare from exile one who has committed murder unintentionally. Rather, he must be exiled.

The source of this prohibition is G‑d's statement1 (exalted be He), "If one has fled to a refuge city, do not take ransom [to allow him to return and live in the land...]"

The details of this mitzvah are explained in tractate Makkos.