Negative commandment · Lo Ta’aseh #66 of 613
Not to leave a corpse that was hung on the gallows
שלא ילין הצלוב על העץ
The verse · Devarim 21:23
לֹא־תָלִין נִבְלָתוֹ עַל־הָעֵץ כִּי־קָבוֹר תִּקְבְּרֶנּוּ בַּיּוֹם הַהוּא כִּי־קִלְלַת אֱלֹהִים תָּלוּי וְלֹא תְטַמֵּא אֶת־אַדְמָתְךָ אֲשֶׁר ה׳ אֱלֹהֶיךָ נֹתֵן לְךָ נַחֲלָה
“his body shall not remain all night upon the tree, but thou shalt surely bury him that day: (for he that is hanged is accursed of God;) that thy land be not defiled, which the Lord thy God gives thee for an inheritance.”
The Rambam’s words
Not to leave a corpse that was hung on the gallows, as [Deuteronomy 21:23] states: "Do not leave his body on the gallows."
שלא ילין הצלוב על העץ, שנאמר "לֹא תָלִין נִבְלָתוֹ עַל הָעֵץ" (דברים כא, כג).
Where in the Mishneh Torah
Hilchot The Sanhedrin and the Penalties within Their Jurisdiction הלכות סנהדרין והעונשין המסורין להם