Deuteronomy 20:10-12

Amplified Bible

¹⁰ “When you advance to a city to fight against it, you shall [first] offer it terms of peace. ¹¹ If that city accepts your terms of peace and opens its gates to you, then all the people who are found in it shall become your forced labor and shall serve you. ¹² However, if it does not make peace with you, but makes war against you, then you shall lay siege to it.