Betterment
شا، الإرشاد رُوِيَ أَنَّ مُدَّةَ دَوْلَةِ الْقَائِمِ تِسْعَ عَشْرَةَ سَنَةً يَطُولُ أَيَّامُهَا وَ شُهُورُهَا عَلَى مَا قَدَّمْنَاهُ وَ هَذَا أَمْرٌ مُغَيَّبٌ عَنَّا وَ إِنَّمَا أُلْقِيَ إِلَيْنَا مِنْهُ مَا يَفْعَلُهُ اللَّهُ تَعَالَى بِشَرْطٍ يَعْلَمُهُ مِنَ الْمَصَالِحِ الْمَعْلُومَةِ جَلَّ اسْمُهُ فَلَسْنَا نَقْطَعُ عَلَى أَحَدِ الْأَمْرَيْنِ وَ إِنْ كَانَتِ الرِّوَايَةُ بِذِكْرِ سَبْعِ سِنِينَ أَظْهَرَ وَ أَكْثَرَ
(The book) ‘Al Irshad’
‘It is reported that the term of the government of Al-Qaim-ajfj would be of nineteen years. Its days and its months would be prolonged, based upon what has been previously cited, and this is a matter hidden from us, and rather it has been cast to us from it what Allah-azwj the Exalted would Do with the conditions He-azwj Knows, from the known betterment, Majestic is His-azwj Name. So, we are not cutting upon any one of the two matters, and even though the reports mentioning seven years are more apparent and many in numbers.[1]
[1] Bihar Al Anwaar – V 52 The book of History – Imam Al-Mahdi-ajfj, Ch 27 H 87