Safinah:
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.