Hebrews 7:21
(For those were made priests without an oath, but this one was made a priest with an oath by him who says of him, The Lord gave his oath, which he will not take back, that you are a priest for ever);
Hebrews 7:17
For it has been witnessed of him, You are a priest for ever after the order of Melchizedek.
1 Samuel 15:29
And further, the Glory of Israel will not say what is false, and his purpose may not be changed: for he is not a man, whose purpose may be changed.
Hebrews 6:16-18
For men at all times make their oaths by what is greater; and any argument is ended by the decision of the oath.