Kommentar zu Bereschit 26:33

שבעה [AND HE CALLED IT] SHIBAH (swearing), in allusion to the Covenant (cf. v.31; “And they swear” etc.).

על כן שם העיר באר שבע this was not the same Beer Sheva we read about in connection with Avraham. There were two towns called Beer Sheva, as we know from Kings I 19,3 ויבא באר שבע אשר ליהודה, “he came to Beer Sheva in Yehudah.” [If there had not been another Beer Sheva the additional words “which is in Yehudah” would have been unnecessary. Ed.]

ויקרא אותה שבעה, on account of the oath that Yitzchok and Avimelech had sworn there. Avraham had done the same. (21,31) Even though he had not named the well itself שבעה, he named the entire region Beer Sheva, both on account of the oath and on account of the seven sheep which had been the physical symbol of that oath. Both Avraham and Yitzchok named the event in the presence of Avimelech.