Musnad Ahmad 550
It was narrated that ‘Abdullah bin Muhammad bin `Aqeel said:
`Uthman (رضي الله عنه) was killed in 35 AH and the fitnah (turmoil) lasted for
five years including four months of al-Hasan`s rule.
حَدَّثَنَا زَكَرِيَّا بْنُ عَدِيٍّ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَمْرٍو، عَنْ عَبْدِ اللَّهِ بْنِ مُحَمَّدِ بْنِ عَقِيلٍ، قَالَ قُتِلَ عُثْمَانُ رَضِيَ اللَّهُ عَنْهُ سَنَةَ خَمْسٍ وَثَلَاثِينَ فَكَانَتْ الْفِتْنَةُ خَمْسَ سِنِينَ مِنْهَا أَرْبَعَةُ أَشْهُرٍ لِلْحَسَنِ رَضِيَ اللَّهُ عَنْهُ‏.‏