Hebrews 6:13-18

For when God made the promise to Abraham, since He could swear by no one greater, He swore by Himself, saying, “I WILL SURELY BLESS YOU AND I WILL SURELY MULTIPLY YOU.” And so, having patiently waited, he obtained the promise. For men swear by one greater than themselves, and with them an oath given as confirmation is an end of every dispute. In the same way God, desiring even more to show to the heirs of the promise the unchangeableness of His purpose, interposed with an oath, so that by two unchangeable things in which it is impossible for God to lie, we who have taken refuge would have strong encouragement to take hold of the hope set before us.