Ezra 10:5

Then arose Ezra
From the ground where he lay:

and made the chief priests, and the Levites, and all Israel, to swear
that they should do according to this word:
he took an oath of all that were present to do what was proposed, namely, to put away strange wives and their children:

and they sware;
by means of which they were kept to their word of promise, an oath being a solemn, sacred, thing.