Genesis 17:11

And he received the sign of circumcision, a seal of the righteousness of the faith which he had yet being uncircumcised: that he might be the father of all them that believe, though they be not circumcised; that righteousness might be imputed unto them also:

Circumcise therefore the foreskin of your heart, and be no more stiffnecked.

And he gave him the covenant of circumcision: and so Abraham begat Isaac, and circumcised him the eighth day; and Isaac begat Jacob; and Jacob begat the twelve patriarchs.

And when a stranger shall sojourn with thee, and will keep the passover to the LORD, let all his males be circumcised, and then let him come near and keep it; and he shall be as one that is born in the land: for no uncircumcised person shall eat thereof.

And David sent messengers to Ishbosheth Saul’s son, saying, Deliver me my wife Michal, which I espoused to me for an hundred foreskins of the Philistines.

Then Zipporah took a sharp stone, and cut off the foreskin of her son, and cast it at his feet, and said, Surely a bloody husband art thou to me.

And Joshua made him sharp knives, and circumcised the children of Israel at the hill of the foreskins.