What was it about Yishmael that disturbed Avraham?
Rashi #2 and Ramban: Avraham felt bad about expelling Yishmael. Had Sarah demanded that he expel Hagar, 1 he would have listened to her; but his son - that was a different matter. 2
Rashi #1 and Targum Yonasan: He felt bad that Yishmael had strayed from the right path. 3
To the credit of Avraham, who would not have hesitated on account of his desire for his concubine.
Refer to 21:11:1.2:2.
I.e. he worshipped idols (Targum Yonasan).
QUESTIONS ON RASHI
Rashi writes: "'About his son' - He [now] heard that [Yishmael] had left the proper path. But the simple explanation is...." Why does Rashi cite the Midrash?
Gur Aryeh #1: The whole phrase "about his son" is extra. (The verse could have written, 'It seemed evil in his eyes to send him away.') "Rather it means that something relating to Yishmael himself was bad in his eyes.
Gur Aryeh #2: If sending Yishmael away seemed wrong, Avraham could have simply declined to do so! (HaSh-m had not yet told him to heed Sarah's voice.) Rather, it was Yishmael's deeds that seemed bad.
Rashi writes: "'About his son' - [Yishmael] had left the proper path." If so, why does HaSh-m reassure Avraham with the words, "Let it not seem bad (Al Yeira b'Einecha) about the lad and about your maidservant" (21:12) -Hagar had not left the proper path!
Gur Aryeh #1: Despite the parallel wording, "Al Yeira b'Einecha" (21:12) is not a response to "va'Yeira... b'Einei Avraham." HaSh-m's response is to be understood in the simple sense - do not feel bad about acceding to Sarah's request to send them away.
Gur Aryeh #2: The Midrash is not to be understood that Avraham felt bad only because Yishmael had left the proper path. Rather it seemed wrong to send him away. Avraham wanted to rebuke Yishmael, so he would change his evil ways; sending him away would endure that he would not do Teshuvah.