Sayyiduna Abu Juhayfah (may Allah be pleased with him) said: I was with my paternal uncle in the presence of the Messenger of Allah (peace and blessings be upon him) while he was delivering a sermon. He (peace and blessings be upon him) said: "The affair of my Ummah will remain sound until twelve caliphs have passed," and he (peace and blessings be upon him) said this in a low voice. I asked my uncle, who was in front of me: Dear uncle, what did he (peace and blessings be upon him) say? He said: My son, all of them will be from Quraysh.
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18528