Midrash su Genesi 33:19

(Devarim 1:8) "which the L-rd swore to your fathers": Why need it be mentioned (in addition to this) "to Abraham, to Isaac, and to Jacob"? (To stress that) each one was worthy of this in himself. An analogy: A king gives his servant one field as a gift, as it is. The servant goes and improves it, not leaving it as it is, but planting a vineyard and bequeaths it to his son — who does not leave it as it is, but improves it and bequeaths it to his son — who does not leave it as it is, but improves it. Thus, when the Holy One Blessed be He gave the land to our father Abraham, He gave it to him only as it was, viz. (Bereshith 13:17) "Arise, walk in the land in its length and its breadth, for to you shall I give it." Abraham arose and improved it, viz. (Ibid. 21:33) "And he planted a fruit grove in Beersheva." Isaac arose and improved it, viz. (Ibid. 26:12) "And Isaac sowed in that land and he found in that year a hundredfold." Jacob arose and improved it, viz. (Ibid. 33:19) "And he bought the part of the field where he had pitched his tent." If so, why need "to your fathers" be written? If in respect to the oath to the fathers, this is already written. This refers to the covenant with the tribes, viz. (Habakkuk 3:9) "the oaths to the tribes, an enduring word."

“And he bought the part of the field where he had pitched his tent from the sons of Hamor, the father of Shechem, for a hundred kesitas.” (Bereshit 33:19) R’ Yudan bar Simon said: this is one of the three places about which the nations of the world cannot defraud Israel and say ‘this is stolen property in your hands.’ They are – the cave of the Machpela, the Holy Temple and the grave of Yosef. The cave of the Machpela, as it is written “And Abraham listened to Ephron, and Abraham weighed out to Ephron the silver…” (Bereshit 23:16) The Holy Temple, as it is written “And David gave to Ornan for the place shekels of gold weighing six hundred.” (Divre HaYamim I 21:25) The grave of Yosef, as it is written ““And he bought the part of the field where he had pitched his tent…” (Bereshit 33:19)