Exodus 4:22-24

Amplified Bible

²² Then you shall say to Pharaoh, ‘Thus says the Lord, “Israel is My son, My firstborn. ²³ So I say to you, ‘Let My son go so that he may serve Me’; and if you refuse to let him go, behold, I will kill your son, your firstborn.”’”

²⁴ Now it happened at the lodging place, that the Lord met Moses and sought to kill him [making him deathly ill because he had not circumcised one of his sons].^(A)