אַ֣ךְ הַנָּבִ֡יא אֲשֶׁ֣ר יָזִיד֩ לְדַבֵּ֨ר דָּבָ֜ר בִּשְׁמִ֗י אֵ֣ת אֲשֶׁ֤ר לֹֽא־צִוִּיתִיו֙ לְדַבֵּ֔ר וַאֲשֶׁ֣ר יְדַבֵּ֔ר בְּשֵׁ֖ם אֱלֹהִ֣ים אֲחֵרִ֑ים וּמֵ֖ת הַנָּבִ֥יא הַהֽוּא׃
But the prophet, that shall speak a word presumptuously in My name, which I have not commanded him to speak, or that shall speak in the name of other gods, that same prophet shall die.’
Sifrei Devarim
(Devarim 18:20) "then he shall be put to death": by the unqualified "death penalty" of the Torah, i.e., strangulation.