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Hadith, the teachings and sayings of the Prophet Muhammad, was the Islamic tradition in which Ali al-Sajjad held authority. As the fourth Shia Imam, he was renowned for his extensive knowledge and understanding of Hadith, which he transmitted and interpreted to his followers. His teachings and interpretations played a significant role in shaping Shia Islamic thought and practice, particularly in the areas of jurisprudence, theology, and spirituality.