Al-Kāfi - Volume 1 > Tacit and Explicit Testimony as proof of abu Ja‘far al-Thani’s (the second) (a.s.) Divine Authority over the people after abu al-Hassan al-Rida (a.s.)
Hadith #1

1ـ عَلِيُّ بْنُ مُحَمَّدٍ عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ مُحَمَّدِ بْنِ الْوَلِيدِ عَنْ يَحْيَى بْنِ حَبِيبٍ الزَّيَّاتِ قَالَ أَخْبَرَنِي مَنْ كَانَ عِنْدَ أَبِي الْحَسَنِ الرِّضَا (عَلَيْهِ السَّلام) جَالِساً فَلَمَّا نَهَضُوا قَالَ لَهُمُ الْقَوْا أَبَا جَعْفَرٍ فَسَلِّمُوا عَلَيْهِ وَأَحْدِثُوا بِهِ عَهْداً فَلَمَّا نَهَضَ الْقَوْمُ الْتَفَتَ إِلَيَّ فَقَالَ يَرْحَمُ الله الْمُفَضَّلَ إِنَّهُ كَانَ لَيَقْنَعُ بِدُونِ هَذَا.

1. Ali ibn Muhammad has narrated from Sahl ibn Ziyad from Muhammad ibn al-Walid from Yahya ibn Habib al-Zayyat who has said the following. “A man who was present in a meeting (of people) with abu al-Hassan al-Rida (a.s.) spoke to me of the information herein below. “When people readied themselves to leave the meeting the Imam (a.s.) said to them, “Meet abu Ja‘far (a.s.), (before you leave), offer to him greeting and renew your covenant with him.” When left, he (the Imam) said to me, “May Allah grant well-being to al-Mufaddal, he would have believed (in the succeeding Imam) without it (the command to renew their covenant)”.