Muhammad Ibn Abdi l-Malik At-Tabban writes:

سُـئِـلَ (الـشَّـرِيـفُ الْـمُـرْتَـضَـى) رَضِـيَ الـلَّـهُ عَـنْـهُ عَـنِ الْـحَـالِ بَـعْـدَ إِمَـامِ الـزَّمَـانِ عَـلَـيْـهِ الـسَّـلَامُ فِـي الْإِمَـامَـةِ فَـقَـالَ إِذَا كَـانَ الْـمَـذْهَـبُ الْـمَـعْـلُـومُ أَنَّ كُـلَّ زَمَـانٍ لَا يَـجُـوزُ أَنْ يَـخْـلُـوَ مِـنْ إِمَـامٍ يَـقُـومُ بِإِصْـلَاحِ الـدِّـيـنِ وَمَـصَـالِـحِ الْـمُـسْـلِـمِـيـنَ وَلَـمْ يَـكُـنْ لَـنَـا بِـالـدَّلِـيـلِ الـصَّـحِـيـحِ أَنَّ خُـرُوجَ الْـقَـائِـمِ يُـطَـابِـقُ زَوَالَ الـتَّـكِـلِـيـفِ فَـلَا يَـخْـلُـو الـزَّمَـانُ بَـعْـدَهُ عَـلَـيْـهِ الـسَّـلَامُ مِـنْ أَنْ يَـكُـونُ فِـيـهِ إِمَـامٌ مُـفْـتَـرَضُ الـطَّـاعَـةِ أَوْ لَـيْـسَ يَـكُـونُ فَـإِنْ قُـلْـنَـا بِـوُجُـودِ إِمَـامٍ بَـعْـدَهُ خَـرَجْـنَـا مِـنَ الْـقَـوْلِ بِـالْاِثْـنَـيْ عَـشَـرِيَّـةِ وَإِنْ لَـمْ نَـقُـلْ بِـوُجُـودِ إِمَـامٍ بَـعْـدَهُ أَبْـطَـلْـنَـا الْأَصْـلَ الَّـذِي هُـوَ عِـمَـادُ الْـمَـذْهَـبِ وَهُـوَ قُـبْـحِ خُـلُـوِّ الـزَّمَـانِ مِـنَ الْإِمَـامِ

“He (Ash-Sharif Al-Murtada) was asked, may God be pleased with him, about the condition after the Imam of the time (a.) regarding the leadership. Thus it was said: “If the common confession is that there can be no time without a leader who puts the religion and affairs of Muslims in order, and we have no valid proof that the appearance of the Riser (Qa’im) corresponds to the end of the imposition (Taklif), then the time after him is not without the fact that there is a leader to whom obedience is a obligation, or there will not be. But if we profess the existence of a leader after him, we leave the confession that we are the Shiites of the twelve, and if we do not confess the existence of a leader after him, we declare the principle as false which is the pillar of confession, and this is the insult of being free of a leader for a time.”

فَـأَجَـابَ رَضِـيَ الـلَّـهُ عَـنْـهُ وَقَـالَ إِنَّـا لَا نَـقْـطَـعُ عَـلَـى مُـصَـادَفَـةِ خُـرُوجِ صَـاحِـبِ الـزَّمَـانِ مُـحَـمَّـدِ بْـنِ الْـحَـسَـنِ عَـلَـيْـهِـمَـا الـسَّـلَامُ زَوَالَ الـتَّـكْـلِـيـفِ بَـلْ يَـجُـوزُ أَنْ يَـبْـقَـى الْـعَـالَـمُ بَـعْـدَهُ زَمَـانًـا كَـثِـيـرًا وَلَا يَجُـوزُ خُـلُـوُّ الـزَّمَـانِ بَـعْـدَهُ مِـنَ الْأَئِـمَّـةِ وَيَـجُـوزُ أَنْ يَـكُـونَ بَـعْـدَهُ عِـدَّةُ أَئِـمَّـةٍ يَـقُـومُـونَ بِـحِـفْـظِ الـدِّيـنِ وَمَـصَـالِـحِ أَهْـلِـهِ وَلَـيْـسَ يَـضُـرُّنَـا ذَلِـكَ فِـيـمَـا سَـلَـكْـنَـاهُ مِـنْ طُـرُقِ الْإِمَـامَـة لِأَنَّ الَّـذِي كُـلِّـفْـنَـا إِيَّـاهُ وَتَـعَـبَّـدْنَـا مِـنْـهُ أَنْ نَـعْـلَـمَ إِمَـامَـةَ هَـؤُلَاءِ الْاِثْـنَـيْ عَـشَـرَ وَنُـبَـيِّـنُـهُ بَـيَـانًـا شَـافِـيًـا إِذْ هُـوَ مَـوْضِـعُ الْـخِـلَافِ وَالْـحَـاجَـةِ وَلَا يُـخْـرِجُـنَـا هَـذَا الْـقَـوْلُ عِـنِ الـتَّـسَـمِّـي بِـالْاِثْـنَـي عَـشَـرِيَّـةِ لِأَنَّ هَـذَا الْاِسْـمَ عِـنْـدَنَـا يُـطْـلَـقُ عَـلَـى مَـنْ يُـثْـبِـتُ إِمَـامَـةَ اثْـنَـيْ عَـشَـرَ إِمَـامًـا وَقَـدْ أَثْـبَـتْـنَـا نَـحْـنُ وَلَا مُـوَافِـقَ لَـنَـا فِـي هَـذَا الْـمَـذْهَـبِ فَـانْـفَـرَدْنَـا نَـحْـنُ بِـهَـذَا الْاِسْـمِ دُونَ غَـيْـرِنَـا

“Then he replied that God was pleased with him and said: “We do not assume with certainty that the end of the imposition (Taklif) will come at the same time as the appearance of the ruler of the time, Muhammad Ibn Hasan (a.), but it is possible that the world after him will last a long time. It is not possible that the time after him remains without leaders. It is possible that after him there will be a number of leaders who will protect the religion and interests of their dependants, and this cannot harm us with regard to the paths we have chosen for leadership, because that which is enjoined on us and from which we devote ourselves to the service (of God) is that we know of the leadership of these twelve. We make a clear declaration, because this is the core of the conflict and need. This confession does not allow us to abandon the title as Shiites of the twelve, since in our case this title is held by the one who acknowledges the leadership of twelve imams, and we have acknowledged it, while nobody else acknowledged it in this confession. Thus we distinguished ourselves with this title alone, to the exclusion of others.” [Rasa’il-ul-Murtada, Volume 3, pages 145 – 146]