It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "When the two 'Atiqs, the 'Atiq of the Arabs and the 'Atiq of the Romans, become kings, great battles will take place at their hands."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13764