Leader of Islamic Revolution Ayatollah Seyyed Ali Khamenei attended a ritual ceremony in the holy shrine of Imam Reza (PBUH) in Mashhad on Sunday, his official website reported. Imam Reza (PBUH), the eighth Imam in the Twelver Shia Islam, was martyred after being poisoned by Abbasid Caliph Ma'mun in 818 AD. The highly revered religious site hosts millions of pilgrims annually from across the Muslim world. Ayatollah Khamenei appoints the custodian of the Astan Qods Razavi, an organization that oversees the shrine affairs. Hojjatoleslam Ebrahim Raeisi assumed that post in March last year after former custodian, Ayatollah Abbas Vaez Tabasi, passed away. Raeisi ran in the May presidential vote on behalf of the conservative camp, but failed to prevent the reelection of moderate President Hassan Rouhani.