It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: The Day of Judgment will not be established until two great armies fight each other; there will be much bloodshed between them and both will claim the same cause.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 10864