Passage Numbers 31:17–18
The argument gathers the passages in which Israel is told to wipe out whole populations. In Numbers 31:17-18 Moses orders every male child and every woman who has been with a man to be killed, while the young girls are kept alive for the Israelites, and the count of these in Numbers 31:35 comes to 32,000. Deuteronomy 20:16 says that in the cities given as an inheritance nothing that breathes is to be left alive.
Joshua 6:21 reports that at Jericho every man, woman, child, ox, sheep and donkey was devoted to destruction, and Joshua 10:28 says that at Makkedah Joshua left no one remaining. The argument is that a book which commands and reports this has no standing to accuse others of cruelty.
Now therefore, kill every male among the little ones, and kill every woman who has known man by lying with him. But all the young girls who have not known man by lying with him keep alive for yourselves.
Numbers 31:17-18
But in the cities of these peoples that the LORD your God is giving you for an inheritance, you shall save alive nothing that breathes,
Deuteronomy 20:16
Then they devoted all in the city to destruction, both men and women, young and old, oxen, sheep, and donkeys, with the edge of the sword.
Joshua 6:21
Source: see Credits and references (no. 25, p. 24).