פּירוש אויף בראשית 24:9

תחת ירך אברהם, “under the thigh of Avraham.” Joseph, when asked by his father to swear that he would not bury him in Egypt but with his father and grandfather in Machpelah, did not do so, as he considered such behavior not respectful toward his father, even though he had requested him to swear. (Compare Genesis 47,2931)

על הדבר הזה, concerning the condition stipulated by Avraham.

וישבע לו על הדבר הזה, he accepted all of Avraham’s conditions as part of his oath.