Exodus 23:18 "Neither shall the fat of My sacrifice remain until the morning"

The Passover sacrifice is offered on the fourteenth of Nissan, and is eaten that night, the first night of Passover, which is the fifteenth of Nisan (the first Seder Night).

This Negative Mitzvah refers to those portions of the Passover Sacrifice which are consumed by fire on the altar. We are cautioned not to leave these portions overnight without burning them on the altar.