Al-Kāfi - Volume 1 > Tacit and Explicit Testimony as proof of abu ‘Abdallah Ja‘far ibn Muhammad al-Sadiq’s (a.s.) Divine Authority over the people after Muhammad ibn Ali ibn al-Husayn (a.s.)
Hadith #6

6ـ أَحْمَدُ بْنُ مِهْرَانَ عَنْ مُحَمَّدِ بْنِ عَلِيٍّ عَنْ فُضَيْلِ بْنِ عُثْمَانَ عَنْ طَاهِرٍ قَالَ كُنْتُ قَاعِداً عِنْدَ ابي جعفر (عَلَيْهِ السَّلام) فَأَقْبَلَ جَعْفَرٌ (عَلَيْهِ السَّلام) فَقَالَ أَبُو جَعْفَرٍ (عَلَيْهِ السَّلام) هَذَا خَيْرُ الْبَرِيَّةِ.

6. Ahmad ibn Mihran has narrated from Muhammad ibn Ali from Fudayl ibn ‘Uthman from who has said the following. “Once I was in the presence of abu Ja‘far (a.s.) that Ja‘far (a.s.) came. Abu Ja‘far (a.s.) said, “This (Ja‘far) is the best of the people.”