ENOfficial
Safina told that he heard the Prophet (ﷺ) 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.
Source: sunnah.com
Other translations
Arabic
وَعَن سفينة قَالَ: سَمِعْتُ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ: «الْخِلَافَةُ ثَلَاثُونَ سَنَةً ثُمَّ تَكُونُ مُلْكًا» . ثُمَّ يَقُولُ سَفِينَةُ: أَمْسِكْ: خِلَافَةَ أَبِي بَكْرٍ سَنَتَيْنِ وَخِلَافَةَ عُمَرَ عَشْرَةً وَعُثْمَانَ اثْنَتَيْ عَشْرَةَ وَعَلِيٍّ سِتَّةً. رَوَاهُ أَحْمَدُ وَالتِّرْمِذِيُّ وَأَبُو دَاوُدَ
sunnah.com