Negative commandment · Lo Ta’aseh #201 of 613
Not to have chametz found [in one's possession during Pesach]
שלא יימצא חמץ
The verse · Shemot 12:19
שִׁבְעַת יָמִים שְׂאֹר לֹא יִמָּצֵא בְּבָתֵּיכֶם כִּי כׇּל־אֹכֵל מַחְמֶצֶת וְנִכְרְתָה הַנֶּפֶשׁ הַהִוא מֵעֲדַת יִשְׂרָאֵל בַּגֵּר וּבְאֶזְרַח הָאָרֶץ
“Seven days shall there be no leaven found in your houses: for whoever eats that which is leavened, even that soul shall be cut off from the congregation of Yisra᾽el, whether he be a stranger, or born in the land.”
The Rambam’s words
Not to have chametz found [in one's possession during Pesach], as [Exodus 13:7] states: "No chametz may be found in your homes."
שלא יימצא חמץ, שנאמר "שאור, לא יימצא בבתיכם" (שמות יב,יט).
Why · Sefer HaChinuch #11
That chametz not be found in our possession on Pesach
“From the roots of this commandment are so that the Jews will remember forever the great miracles that G-d performed for them during the exodus from Egypt.”
Who & when
“And [it] is practiced by males and females in every place and at all times.”
Where in the Mishneh Torah
Hilchot Leavened and Unleavened Bread הלכות חמץ ומצה