Hebrews 6:16-18

16Now when people take an oath, they call on someone greater than themselves to hold them to it. And without any question that oath is binding.

17God also bound himself with an oath, so that those who received the promise could be perfectly sure that he would never change his mind.

18So God has given both his promise and his oath. These two things are unchangeable because it is impossible for God to lie. Therefore, we who have fled to him for refuge can have great confidence as we hold to the hope that lies before us.