Hebrews 6:13-18

For when God made a promise to Abraham, because He could swear by no one greater, He swore by Himself, saying, “Surely blessing I will bless you, and multiplying I will multiply you.” And so, after he had patiently endured, he obtained the promise. For men indeed swear by the greater, and an oath for confirmation is for them an end of all dispute. Thus God, determining to show more abundantly to the heirs of promise the immutability of His counsel, confirmed it by an oath, that by two immutable things, in which it is impossible for God to lie, we might have strong consolation, who have fled for refuge to lay hold of the hope set before us.