Complex sentence: Abu Hamzah Al-Thumali, who was a companion of three Shia Imams, received it from Imam al-Sajjad and was the principal narrator of the work.
Split into simpler sentences: Abu Hamzah Al-Thumali who was a companion of three Shia Imams, received it from Imam al-Sajjad. He was the principal narrator of the work.