משך חכמה — ויקברו אותו יצחק וישמעאל

Q — Why is Yitzchak listed before his older brother Yishmael at Avraham's burial, and what exactly was the teshuvah of Yishmael that Chazal derive from this?

A — Yishmael's sin (per Sforno) was mocking the משתה of Yitzchak by claiming Sarah had conceived from Avimelech — i.e. denying Yitzchak's legitimacy as the son of the gevirah; his teshuvah was acknowledging Yitzchak as Avraham's true heir and yielding precedence to him at the burial, thereby accepting the very ייחוס he had once denied.