Numbers 21:34

אל תירא אתו FEAR HIM NOT — God said this concerning Og but not about Sihon (cf v. 23), because Moses feared to wage battle, perhaps the merit of Abraham with whom Og had been associated would stand up (i.e., be an advocate) for him, as it is said, (Genesis 14:13) “And the one who escaped came [and told it to Abraham]” — this was Og who had escaped from the Rephaim whom Chedoladmar and his allies had smitten in Ashoreth Karnaim (Genesis 14:5), as it is said, (Deuteronomy 3:11). "For only Og king of Bashan was left of the remnant of the Rephaim" (cf. Midrash Tanchuma, Chukat 25, Niddah 61a).

וַיֹּ֨אמֶר יְהֹוָ֤ה אֶל־מֹשֶׁה֙ אַל־תִּירָ֣א אֹת֔וֹ כִּ֣י בְיָדְךָ֞ נָתַ֧תִּי אֹת֛וֹ וְאֶת־כׇּל־עַמּ֖וֹ וְאֶת־אַרְצ֑וֹ וְעָשִׂ֣יתָ לּ֔וֹ כַּאֲשֶׁ֣ר עָשִׂ֗יתָ לְסִיחֹן֙ מֶ֣לֶךְ הָֽאֱמֹרִ֔י אֲשֶׁ֥ר יוֹשֵׁ֖ב בְּחֶשְׁבּֽוֹן׃

And the Lord said to Moshe, Fear him not: for I have delivered him into thy hand, and all his people, and his land; and thou shalt do to him as thou didst to Siĥon king of the Emori, who dwelt at Ḥeshbon.