Genesis 21:4

21:4 When his son Isaac was eight days old, ¹  Abraham circumcised him just as God had commanded him to do. ² 

Genesis 17:23

17:23 Abraham took his son Ishmael and every male in his household (whether born in his house or bought with money) ³  and circumcised them ⁴  on that very same day, just as God had told him to do.

[21:4]  ¹ tn Heb “Isaac his son, the son of eight days.” The name “Isaac” is repeated in the translation for clarity.

[21:4]  ² sn Just as God had commanded him to do. With the birth of the promised child, Abraham obeyed the Lord by both naming (Gen 17:19) and circumcising Isaac (17:12).

[17:23]  ³ tn Heb “Ishmael his son and all born in his house and all bought with money, every male among the men of the house of Abraham.”

[17:23]  ⁴ tn Heb “circumcised the flesh of their foreskin.” The Hebrew expression is somewhat pleonastic and has been simplified in the translation.