Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "When Kisra perishes, there will be no Kisra after him, and when Caesar perishes, there will be no Caesar after him. By the One in whose hand my soul is! You will spend the treasures of both of them in the path of Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18602