Abu Dawud
Trials And Fierce Battles
Book Number: 030 / Hadith Number: 4252
Narated By Abdullah ibn Amr ibn al-'As : The Prophet (pbuh) said: There will be civil strife which wipe out the Arabs, and their slain will go to Hell. During it the tongue will be more severe than blows of the sword.
Abu Dawud said: Al-Thawri transmitted it from Laith, from Tawus on the authority of al-A'jam.