There is a beautiful Chasam Sofer on this daf when the gemara says that one should not give their inheritance to a "good son" and take away from a "bad son" because there may be a grandson from the "bad son" who deserves it.
In this weeks parhsa, the pesukim describe that Avraham was very reluctant to throw out Yishmael and leave him out of yerusha until Hashem told him to listen to Sarah since she spoke with prophecy. Why does the fact that it was nevuah make a difference? But more basic, why did Avraham want Yishmael to inherit since he was committing aveiros?
The Chasam sofer explains that Avraham was concerned that Yishmael may have a child who deserves the inheritance and didn't want to disown him as we find in the gemara. Sarah told Avraham b'nevuah that no one good will come out from Yishmael, so then Avraham listened to her since the concern of the gemara no longer applies.
My question on the Chasam Sofer is, Why did Avraham have to wait until a direct instruction from Hashem to listen to Sarah, the prophecy of Sarah that no one good will come from Yishmael should have convinced Avraham without a specific tzivuy from Hashem?
Perhaps Avraham was still concerned because we find that Yishmael's existence was only because "b'asher hu sham", and this is why Yishmael did not die from his illness. Just as we find from the concept of "ba'asher hu sham" that Yishmael cannot be judged based on the prophecy of what his future actions will be, so too here Avraham did not want to judge the children of Yishmael based on Sarah's prophecy that they will turn out to be bad (rather look at the present, which allows for the possibility to have a good grandchild even from a bad son, as we see the gemara considers this very viable). Only after Hashem explicitly tells Avraham to listen to Sarah is he convinced to disown him.
