Beowulf attributes Unferth's ill-considered comments to too much ale but then goes on to make a harsh prediction for Unferth. What is Beowulf's prediction?

He says that Unferth will not kill Grendel but he will. He says he hears that Unferth killed his brothers.

From the text:

"You killed your own kith and kin, so for all your cleverness and quick tongue, you will suffer damnation in the depths of hell."