Negative commandment · Lo Ta’aseh #200 of 613
Not to have chametz seen [in one's possession during Pesach]
שלא ייראה חמץ
The verse · Shemot 13:7
מַצּוֹת יֵאָכֵל אֵת שִׁבְעַת הַיָּמִים וְלֹא־יֵרָאֶה לְךָ חָמֵץ וְלֹא־יֵרָאֶה לְךָ שְׂאֹר בְּכׇל־גְּבֻלֶךָ
“Unleavened bread shall be eaten for seven days; and there shall no leavened bread be seen with thee, neither shall leaven be seen with thee in all thy borders.”
The Rambam’s words
Not to have chametz seen [in one's possession during Pesach], as [Exodus 13:7] states: "No chametz and no leaven may be seen in your territories."
שלא ייראה חמץ, שנאמר "לא ייראה לך חמץ" (שמות יג,ז).
Who & when
“And [it] is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Leavened and Unleavened Bread הלכות חמץ ומצה