Safina told that he heard the Prophet say, "The Caliphate will last thirty years, then there will be a kingdom." Then Safina was saying:Calculate Abu Bakr's Caliphate as two years, `Umar's as ten, `Uthman's as twelve, and `Ali's as six. Ahmad, Tirmidhi and Abu Dawud transmitted it.
Hadith Referenceمشكوة المصابيح / كتاب الفتن / 5395
Hadith Gradingالألبانی:حسن | زبیر علی زئی:إسناده حسن
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «إسناده حسن، رواه أحمد (5/ 220. 221 ح 22264) و الترمذي (2226 وقال: حسن) و أبو داود (4646)»