Al-Kāfi - Volume 1 > Tacit and Explicit Testimony as proof of abu Muhammad al-Hassan ‘s (a.s.) Divine Authority over the people after Ali ibn Muhammad (a.s.)
Hadith #13

13ـ عَلِيُّ بْنُ مُحَمَّدٍ عَمَّنْ ذَكَرَهُ عَنْ مُحَمَّدِ بْنِ أَحْمَدَ الْعَلَوِيِّ عَنْ دَاوُدَ بْنِ الْقَاسِمِ قَالَ سَمِعْتُ أَبَا الْحَسَنِ (عَلَيْهِ السَّلام) يَقُولُ الْخَلَفُ مِنْ بَعْدِيَ الْحَسَنُ فَكَيْفَ لَكُمْ بِالْخَلَفِ مِنْ بَعْدِ الْخَلَفِ فَقُلْتُ وَلِمَ جَعَلَنِيَ الله فِدَاكَ فَقَالَ إِنَّكُمْ لا تَرَوْنَ شَخْصَهُ وَلا يَحِلُّ لَكُمْ ذِكْرُهُ بِاسْمِهِ فَقُلْتُ فَكَيْفَ نَذْكُرُهُ فَقَالَ قُولُوا الْحُجَّةُ مِنْ آلِ مُحَمَّدٍ عَلَيْهم السَّلام.

13. Ali ibn Muhammad has narrated from the person he mentioned from Muhammad ibn Ahmad al-‘Alawi from Dawud ibn al-Qasim who has said the following. “I heard abu al-Hassan (a.s.) saying, ‘The succeeding (Imam) after me will be al-Hassan. How will your dealing be with the succeeding (Imam) of the succeeding (Imam)?” I then said, “Why will that be so, may Allah take my souls in service for your cause?” He said, “You will not see him in person. It will not lawful for you to pronounce his name.” I then asked, “How then will we speak of him?” He said, “Say, ‘The Divine Authority from the family of Muhammad (s.a).”