solemnly swear

"But you do solemnly swear never to say a word?"

We solemnly swore not to make a break for the border.

I solemnly swear to tell the whole truth, and nothing but the truth.

I solemnly swear to stay away from the furnace room.

But on receiving this award, you solemnly swear to never rap again.

Each executive raised his right hand and solemnly swore to tell the whole truth about his business.

"I solemnly swear this is not going to be a call to a reporter or anyone who will call one."

Each of them solemnly swore: "I am not a guide.

He is led to the center of the room, raises his right hand and is solemnly sworn in.

Anthony swore solemnly that nothing should prevent him keeping the engagement.