الكافي 1/4/124/9

9. Ali ibn Muhammad and Muhammad ibn abu ‘Abdallah have narrated from Ishaq ibn Muhammad al-Nakha‘i who has said that narrated to me Sufyan ibn Muhammad al-Duba‘i who has said the following. “I wrote to abu Muhammad and asked him about the meaning of the word al-Walija (relied) in the words of Allah, the Most High. “Do you think that God will not make any distinction between those of you who have fought for His cause and have relied on no one other than God, His Messenger, and the faithful ones, and other people?. .” (9:16) I said to myself, not in the letter, “To who does the believers refer in this verse “? The answer came as this. The Walija refers to a person who would be appointed in place of the Leader with Divine Authority. You have said to yourself “To who the believers refers in this verse”? They are the Imams who ask Allah to grant security to the people and He grants their request.”