פירוש על יהושע 11:13

Remained with their walls intact. Their walls were not destroyed like Yericho, whose walls fell, and similarly Ai, as it is said, “[And Yehoshua burned Ai] and made it into a mound forever, a ruin.”³See Chapter 8:28 above.

The only exception was Chatzor. He burned it because of a traditional command. Moshe so commanded and transmitted it to him. This is found in Bereishis Rabba on the Sidrah of “And Yaakov sent.”⁴This command to destroy Chatzor is not written in the Torah. Moshe received this command orally on Mount Sinai and transmitted it to Yehoshua, who fulfilled it.