Hebrews 6:13-17

13For when God made promise to Abraham, because he could swear by no greater, he swore by himself, 14Saying, Surely blessing I will bless thee, and multiplying I will multiply thee. 15And so, after he had patiently endured, he obtained the promise. 16For men verily swear by the greater: and an oath for confirmation is to them an end of every dispute. 17In the same way God, willing more abundantly to show to the heirs of promise the immutability of his counsel, confirmed it by an oath:1