Hebrews 6:17-19

Wherein God, being minded to show more abundantly unto the heirs of the promise the immutability of his counsel, interposed with an oath; that by two immutable things, in which it is impossible for God to lie, we may have a strong encouragement, who have fled for refuge to lay hold of the hope set before us: which we have as an anchor of the soul, a hope both sure and stedfast and entering into that which is within the veil