For Hamidreza Al Al-Mahdi the most important reason why he believed in this Call is one person only, the second Mahdi Aba Al-Sadiq (pbuh).
Hamidreza Al Al-Mahdi lived with Aba Al-Sadiq (pbuh) for 10 years in which he saw the divine leader whom he learnt from. He has never seen anyone as pious and as truthful as him (pbuh).