Torah Portion: Mishpatim
You shall not offer the blood of My feast-offering upon leavened bread (Shemos 23:18).
It is a negative commandment that we not slaughter the Pesach lamb on the fourteenth of Nissan while the chametz (leavened bread) is still in our possession, before midday. Our Sages derived this from the verse, You shall not offer the blood of My feast-offering upon leavened bread (Shemos 23:18), which they explained refers to the sacrificing of the Pesach lamb while one still owns chametz. Also included in the mitzvah is that chametz not be in the possession of any of the following people: the one who will be slaughtering the offering, the one who will throw its blood on the Altar, the one who will offer its fats, and any of the registered members of the group.
Among the roots of the mitzvah is the idea that setting [separate] times for every [mitzvah] guarantees their fulfillment. Therefore, with regard to Passover — which is extremely important for the perpetuation of our religion, as explained above (in Mitzvah 21) — the Holy One commanded that we fulfill it with order and with set times for each of its elements. We were therefore told to first banish the chametz, which is repulsive in our eyes during Passover time, and only then commence the Pesach offering, which begins the celebration of the good festival.
This mitzvah applies when the Holy Temple stands to both men and women. One who transgresses this and retains chametz in his possession during that time, though he transgresses a prohibition, [his] Pesach offering is not disqualified as a result of this.