God Appeared to Abraham and remembered the covenant between Abraham and God. God changed the name of Abram to Abraham which means father of many nations, Sarai to Sarah mother of many nations. God said to Abraham every male child of 8 days old shall circumcise flesh of the fore skin, it is applicable to male child born in Abraham's house as well as children bought with money, for the remembrance of everlasting covenant.
Abraham and his Ismael, and all born in his house and others bought with money were circumcised the flesh of foreskin on the same day. Abraham was 99 years when he was circumcised.
God said to Abraham, Ismael also will be blessed exceedingly and he will be fruitful. and 12 princess will come from Ismael and he will be a great nation. Ismael was 13 years old when he was circumcised.
" God blessed Abraham and Sarah to be the Father and Mother of many nations. God blessed Ismael also to be a great nation. "
~ Genesis 17