Or HaChaim on Genesis 17:23/אור החיים על בראשית י״ז:כ״ג

1 ויקח אברהם את ישמעאל בנו. Abraham took his son Ishmael, etc. Inasmuch as Ishmael had attained maturity, (he was 13 years of age) Abraham had "to take him," i.e. convince him, not merely order him to submit. The same applied to all the other members of his household who were no longer minors. Abraham was anxious that G'd's commandment to become circumcised would be accepted willingly.

2כאשר דבר אתו אלוקים, as G'd had told him to. We need to know why the Torah added these last few words. After all, anyone who reads the passage is aware that this is exactly what Abraham did. Perhaps the Torah wanted to tell us that the efforts Abraham made to have all the people concerned be circumcised willingly was what G'd had told him to do.

3Possibly, the Torah testified to the fact that Abraham complied with G'd's instructions immediately, without any delay. The Torah credited Abraham with the manner in which he related to any of G'd's demands upon him.

4Avodah Zarah 27 understands the repetition of המול ימול in 17,13 to mean that he who circumcises others must himself first have been circumcised. Perhaps this is what is meant by the words: "as He commanded him to do," i.e. Abraham circumcised himself first before he circumcised anyone else. If we accept this explanation we do no longer have to search for a reason why the Torah did not specifically mention that Abraham circumcised himself. There were two reasons why it is assumed that Abraham was the first to circumcise himself. 1) It was his nature to comply with any commandment of G'd immediately. Besides, how could he have persuaded others to do something he himself appeared to be afraid of doing? 2) In order for his circumcision of the members of his household to be halachically valid, he himself had to be circumcised first.

5When the Torah told us in verse 24 that Abraham was circumcised, this concerned only the time element. The Torah wanted us to know that just as Ishmael allowed imself to be circumcised at 13 years of age, so Abraham was 99 years of age. [The letter ו in the word ואברהם in that verse was necessary because it interrupts the story of Ishmael's circumcision. The Torah wanted to mention Abraham's circumcision before that of Ishmael; this is why it had to insert verse 24. Ed.]