Conquest of Tabaristan

Ali bin Muhammad Madaini narrates that Tabaristan was conquered in the era of Hazrat Uthman (ra) in 30 AH by Hazrat Saeed (ra) bin Aas. A battle ensued and the fort was captured [by the Muslims].

(Muhammad Ibn Jarir al-Tabari, Tarikh al-Tabari, Vol. 5, Sanah 30 [Beirut, Lebanon: Dar al-Fikr, 1998], pp. 102-103)