Hebrews 6:15 WEB

¹³  For when God made a promise to Abraham, since he could swear by none greater, he swore by himself,

¹⁴  saying, 'Most surely I will bless you, and I will surely multiply you.'

¹⁵  Thus, having patiently endured, he obtained the promise.

¹⁶  For men indeed swear by a greater one, and in every dispute of theirs the oath is final for confirmation.

¹⁷  In this way God, being determined to show more abundantly to the heirs of the promise the immutability of his counsel, interposed with an oath;