Commentaire sur La Genèse 16:15

'ויקרא אברם שם וגו AND ABRAM CALLED THE NAME [OF HIS SON] etc. — Although Abram had not heard the words of the angel when he said to Hagar “and thou shalt call his name Ishmael”, yet the Holy Spirit rested upon him and he called him Ishmael.

שם בנו אשר ילדה הגר ישמעאל, he was aptly called by that name both from Avram's point of view and from Hagar's point of view. Avraham prayed on behalf of his son Yishmael in 17,20, whereas Hagar's prayer had been heard as confirmed to her by the angel.

ויקרא אברם, even though the angel had instructed Hagar what name to give to the son she would bear, she conveyed this message to Avram, so that both she and Avram called her son Ishmael, in accordance with the angel's instructions. We find a similar situation in Genesis 4,25 and (Genesis 5,3) when Adam's third son was born, where the Torah tells us that both Chavah and Adam called him Sheth. On other occasions we find that father and mother named the same child differently, such as Rachel calling her youngest son בן אוני, whereas Yaakov call him .בנימין (Genesis 35,18)