Genesis 17: 9 - 11:  "God further said to Abraham, 'As for you, you and your offspring to come throughout the ages shall keep My covenant.  Such shall be the covenant between Me and you and your offspring to follow which you shall keep: every male among you shall be circumcised.

You shall circumcise the flesh of your foreskin, and that shall be the sign of the covenant between Me and you.   And throughout the generations, every male among you shall be circumcised at the age of eight days.'"

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