במדבר כ:כ פירוש: רש״י, ספורנו, Siftei Chakhamim וחזקוני

וביד חזקה AND WITH A STRONG HAND — relying upon our ancestors’ assurance: (Genesis 27:22) “and the hands are the hands of Esau” (cf. Midrash Tanchuma, Beshalach 9 on בשלח)

ויצא אדום לקראתו, to face them at the border.

With our grandfather’s assurance. For if not so, why does it say “a strong hand.” Any massive number of people constitutes a strong hand.