It is narrated from Sayyiduna Jabir bin Samurah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "This Ummah will remain upright in its affairs and dominant over its enemy until twelve caliphs have passed among them, all of them from Quraysh." When he (peace and blessings be upon him) returned to his house, Quraysh came to him (peace and blessings be upon him) and asked: "Then what will happen?" He (peace and blessings be upon him) said: "Then there will be turmoil (harj)."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2046