Positive commandment · Mitzvat Aseh #228 of 613
For a court to execute by burning [the condemned] with fire
להיות בית דין שורפין באש
The verse · Vayikra 20:14
וְאִישׁ אֲשֶׁר יִקַּח אֶת־אִשָּׁה וְאֶת־אִמָּהּ זִמָּה הִוא בָּאֵשׁ יִשְׂרְפוּ אֹתוֹ וְאֶתְהֶן וְלֹא־תִהְיֶה זִמָּה בְּתוֹכְכֶם
“And if a man take a wife and her mother, it is wickedness: they shall be burnt with fire, both he and they; that there be no wickedness among you.”
The Rambam’s words
For a court to execute by burning [the condemned] with fire, as [Leviticus 20:14] states: "They shall burn him and them with fire."
להיות בית דין שורפין באש, שנאמר: "באש ישרפו אותו, ואתהן" (ויקרא כ,יד).
Who & when
“And this commandment is practiced by males, as judgment is for them; and only in the Land of Israel, as it is the place of judgment.”
Where in the Mishneh Torah
Hilchot The Sanhedrin and the Penalties within Their Jurisdiction הלכות סנהדרין והעונשין המסורין להם