Musnad Ahmad 28:502

Aswad ibn Amir narrated to us, Hammad ibn Salamah narrated to us, from Layth, from Tawus, from Ziyad ibn Simakush, from Abdullah ibn Amr, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "There will be a tribulation that will cleanse the Arabs; its slain are in the Fire. The tongue in it is more severe than the strike of the sword."