Al-Kāfi - Volume 1 > All the Imams (a.s.) rise for and with authority of Allah, the Most High and guide to Him Allah
Hadith #3

3ـ عَلِيُّ بْنُ مُحَمَّدٍ عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ مُحَمَّدِ بْنِ الْحَسَنِ بْنِ شَمُّونٍ عَنْ عَبْدِ الله بْنِ عَبْدِ الرَّحْمَنِ عَنْ عَبْدِ الله بْنِ الْقَاسِمِ الْبَطَلِ عَنْ عَبْدِ الله بْنِ سِنَانٍ قَالَ قُلْتُ لابِي عَبْدِ الله (عَلَيْهِ السَّلام) يَوْمَ نَدْعُوا كُلَّ أُناسٍ بِإِمامِهِمْ قَالَ إِمَامِهِمُ الَّذِي بَيْنَ أَظْهُرِهِمْ وَهُوَ قَائِمُ أَهْلِ زَمَانِهِ.

3. Ali ibn Muhammad has narrated from Sahl ibn Ziyad from Muhammad ibn al-Hassan ibn Shammun from ‘Abdallah ibn ‘Abd al-Rahman from ‘Abdallah ibn al-Qasim al-Batal from ‘Abdallah ibn Sinan who has said the following. “I asked abu ‘Abdallah (a.s.) about the meaning of , ‘On the day when We will call every nation with her Imam (leader) . .” (17:71) The Imam (a.s.) said, “It refers to the Imam who is with them and he is al-Qa’im of the people of that time.”