Midrash for Sanhedrin 104:16

אשכחן דקטל עבדא בר חורין מנא לן

it is not from them [the heathens] that we derive the practice. So here too, since the Torah decreed the sword,<span class="x" onmousemove="('comment',' V. Infra. ');">¹⁴</span>

Sifrei Devarim