And the 115th prohibition is that we are forbidden from slaughtering the Pesach offering [when in possession] of leavened bread.

The source of this commandment is G‑d's statement,1 "Do not sacrifice the blood of My [Pesach] offering when in possession of leavened bread." The prohibition is repeated with the wording,2 "Do not slaughter [the blood of My (Pesach) offering when in possession of leavened bread]."

This means that beginning in the afternoon, which is the time for slaughtering the Pesach offering, one may not own leav­ened bread. Anyone performing the slaughter, sprinkling the blood, burning [the fats], or belonging to a group [which will be eating the Pesach offering together3] may not own leavened bread. If one of them owned leavened bread at that time [of doing the action], he is punished by lashes.

The Mechilta4 explains, "The verse, 'Do not slaughter the blood of My (Pesach) offering [when in possession] of leavened bread,' means that you may not slaughter the Pesach sacrifice when the leavened bread is still existing [in your possession]."

The details of this mitzvah are explained in the 5th chapter of Pesachim.5