Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 231
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 231, with English translation by Maimonides (Rambam).
לקבור הנהרג ביומו, שנאמר: "כי קבור תקברנו ביום ההוא" (דברים כא,כג).
To bury [the body of] an executed person on the day of his execution, as [Deuteronomy 21:22] states: "For you shall surely bury him on that day."