Genesis 17:9-11

Amplified Bible

⁹ Further, God said to Abraham, “As for you [your part of the agreement], you shall keep and faithfully obey [the terms of] My covenant, you and your descendants after you throughout their generations. ¹⁰ This is [the sign of] My covenant, which you shall keep and faithfully obey, between Me and you and your descendants after you: Every male among you shall be circumcised. ¹¹ And you shall be circumcised in the flesh of your foreskins, and it shall be the sign (symbol, memorial) of the covenant between Me and you.