Rashi on Genesis
ויתן לו את כל אשר לו AND HE HATH GIVEN TO HIM ALL THAT HE HATH — he showed them the deed of gift.
Rashbam on Genesis
ויתן לו את כל אשר לו, his brother will not share in the inheritance with Yitzchok.
Sforno on Genesis
אחרי זקנתו, this is why this son was beloved for him from the day he was born.