Genesis 21:10

עם בני עם יצחק WITH MY SON, WITH ISAAC —For since this is my son, even though he were not as good as Isaac really is, or if he were as good a man as Isaac really is, even though he were not my son, this one (Ishmael) is not deserving of inheriting with him: how much less is he deserving of inheriting with my son, with Isaac — with one who possesses both these qualities (of being my son and of being the good man Isaac) (Genesis Rabbah 53:11).

וַתֹּ֙אמֶר֙ לְאַבְרָהָ֔ם גָּרֵ֛שׁ הָאָמָ֥ה הַזֹּ֖את וְאֶת־בְּנָ֑הּ כִּ֣י לֹ֤א יִירַשׁ֙ בֶּן־הָאָמָ֣ה הַזֹּ֔את עִם־בְּנִ֖י עִם־יִצְחָֽק׃

So she said to Avraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, with Yiżĥaq.