In Surat Al-Baqara Verse 3 There is Indication to Those Who Believe In The Uprising Of Hazrat Mahdi (as)

Ikmaaluddin:  Shaykh Saduq (r.a.) has narrated from Ibne Mutawakkil from Muhammad Attar from  Ibne  Isa from  Umar  bin Abdul  Aziz  from  more  than  one person from Dawood bin Kathir from Imam Ja’far Sadiq (a.s.) that:

He said with regard to the interpretation of the following verse: “Those who believe in the unseen.” (Surah Baqarah 2:3) “That is regarding those who believe  that the uprising  of the Qaim [Mahdi] is truth.”

[The Promised Mahdi, Allamah Muhammad Baqir al-Majlisi, Biharul Anwar, Volume 13 (Old Edition)/Volumes 51-52-53 (New Edition)]