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 #4

4ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ عَلِيِّ بْنِ الْحَكَمِ عَنْ طَاهِرٍ قَالَ كُنْتُ عِنْدَ ابي جعفر (عَلَيْهِ السَّلام) فَأَقْبَلَ جَعْفَرٌ (عَلَيْهِ السَّلام) فَقَالَ أَبُو جَعْفَرٍ (عَلَيْهِ السَّلام) هَذَا خَيْرُ الْبَرِيَّةِ أَوْ أَخْيَرُ.

4. A number of our people has narrated from Ahmad ibn Muhammad from Ali ibn al-Hakam from Tahir who has said the following. “Once I was in the presence of abu Ja‘far (a.s.) when Ja‘far (a.s.) came. Abu Ja‘far (a.s.) said, “This (Ja‘far ) is the best of the people or the best of best among them.”