The Prophet ﷺ said: The Caliphate of Prophecy will last thirty years; then Allah will give the Kingdom of His Kingdom to anyone He wills. Sa'id told that Safinah said to him: Calculate Abu Bakr's caliphate as two years, 'Umar's as ten, 'Uthman's as twelve and 'Ali so and so. Sa'id said: I said to Safinah: They conceive that 'Ali was not a caliph. He replied: The buttocks of Marwan told a lie.
قَالَ رَسُولُ اللَّهِ ﷺ خِلاَفَةُ النُّبُوَّةِ ثَلاَثُونَ سَنَةً ثُمَّ يُؤْتِي اللَّهُ الْمُلْكَ أَوْ مُلْكَهُ مَنْ يَشَاءُ قَالَ سَعِيدٌ قَالَ لِي سَفِينَةُ أَمْسِكْ عَلَيْكَ أَبَا بَكْرٍ سَنَتَيْنِ وَعُمَرَ عَشْرًا وَعُثْمَانَ اثْنَتَىْ عَشْرَةَ وَعَلِيٌّ كَذَا قَالَ سَعِيدٌ قُلْتُ لِسَفِينَةَ إِنَّ هَؤُلاَءِ يَزْعُمُونَ أَنَّ عَلِيًّا عَلَيْهِ السَّلاَمُ لَمْ يَكُنْ بِخَلِيفَةٍ قَالَ كَذَبَتْ أَسْتَاهُ بَنِي الزَّرْقَاءِ يَعْنِي بَنِي مَرْوَانَ