Mohammad Hossein Boshru'i was born in Boshruyeh in South Khorasan to a wealthy and established family of the town. His father Hajji Mullah Abdullah was a dyer; his mother was a poetess and known for her piety and knowledge. Like most young boys of the era he received a haphazard education, learning a little scripture, reading, writing and basic mathematics. At the age of 12 he left school and pursued higher education, which included lessons in Persian literature and the Qur'an, whilst mastering the art of debate. By 21, he was already a mujtahid and whilst studying in Mashhad he became attracted to the teachings of Shaykh Ahmad and Shaykhism.
According to Mullah Husayn, the Shaykhi leader Sayyid Kazim Rashti, instructed his followers to spread out in search of the Qa'im. On Sayyid Kazim's death, Mulla Husayn spent forty days secluded in prayer, after which he traveled to Bushehr and then to Shiraz. There, on 22 May 1844, he encountered the Báb, who declared to Mulla Husayn that he was the expected Qa'im. Mulla Husayn thus became the first of the Báb's followers. The anniversary of this declaration is observed as a holy day by Bahá'í communities around the world.