Albert Barnes Commentary Exodus 1:22

"And Pharaoh charged all his people, saying, Every son that is born ye shall cast into the river, and every daughter ye shall save alive." — Exodus 1:22 (ASV)

The extreme cruelty of the measure does not involve improbability. Hatred of strangers was always a characteristic of the Egyptians , and was likely to be stronger than ever after the expulsion of an alien race.