Complex sentence: Then, he went to Najaf in 1957, but soon returned back to Mashhad due to his father's unwillingness to let his son stay there and settled in Qom in 1958 where he attended the classes of Seyyed Hossein Borujerdi and Ruhollah Khomeini.
Split into simpler sentences: Then, he went to Najaf in 1957, but soon returned back to Mashhad due to his father's unwillingness to let him stay there. In 1958, he settled in Qom where he attended the classes of Seyyed Hossein Borujerdi and Ruhollah Khomeini.