Why does the Torah seem to imply that Avraham named his son before the bris? First:
וַיִּקְרָא אַבְרָהָם אֶת שֶׁם בְּנוֹ הַנּוֹלַד לוֹ אֲשֶׁר יָלְדָה לּוֹ שָׂרָה יִצְחָק
And Abraham called the name of his son that was born unto him, whom Sarah bore to him, Isaac.
So he called his name Yitzchak, and then the next verse says:
וַיָּמָל אַבְרָהָם אֶת יִצְחָק בְּנוֹ בֶּן שְׁמֹנַת יָמִים כַּאֲשֶׁר צִוָּה אֹתוֹ אֱ־לֹהִים
And Abraham circumcised his son Isaac when he was eight days old, as God had commanded him.
and then they did the Bris (circumcision).
Isn't our Minhag to do the Bris and then name the child undermined by this case?