Hadith

Imam Baqir (pbuh)

و اَللَّهِ مَا تَرَكَ اَللَّهُ أَرْضاً مُنْذُ قَبَضَ آدَمَ عَلَيْهِ اَلسَّلاَمُ إِلاَّ وَ فِيهَا إِمَامٌ يُهْتَدَى بِهِ إِلَى اَللَّهِ

I swear to Allah that He has not, from the day Adam died, left the earth without an Imam who would guide people to the Lord as with divine authority over the servants of the Lord.

al-Kafi, v. 1, p. 178