Rabbi Shimon ben Yochai taught: In wartime, the kosher gentiles should be killed.
(Masechtot Ketanon, Sofrim 15:7)
“He took six hundred chosen chariots (Exodus 14:7)”: Who did the animals drawing these chariots belong to? If you answer that they belonged to the Egyptians, did it not already state, “All the animals of Egypt died”? If you say they were the personal property of Pharaoh, then did it not already state, “Behold, the hand of the Lord is upon your animals of the field”? If you say they were the animals of the Israelites, did it not already state, “Our animals shall go with us, not a hoof will remain behind”? Rather, these animals must have belonged to those who feared the word of the Lord. Thus we find that God-fearers were a problem for Israel. From here Rabbi Shimon ben Yochai says, “The best of the gentiles should be killed.”(Mekihlta d’bei Yishmael, B’Shalach, Vayehi 1:”vayikah shesh”)