Volume 4 · Book 56 · Hadith 805
Narrated Abu Huraira: Allah's Apostle said, "The Day of (Judgment) will not be established till there is a war between two groups whose claims (or religion) will be the same."
— Sahih Bukhari, Volume 4, Book 56: Virtues and Merits of the Prophet (pbuh) and his Companions, Hadith #805