The claim
Ali ibn Abi Talib was among the earliest who narrated and taught.
The evidence
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The chain of transmitters — passage/arbaun-05
A Forty hadith whose chain runs through the household's kin.
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chronicle — work/itmam-al-wafa-fi-sirat-al-khulafa
A paraphrase of Itmam al-Wafa on the caliphs' lives: Ali's standing in narration and judgem'en't, restated faithfully.
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object — object/naal-al-nabi
The preserved sandal — a relic tied to the Prophet's household in memory.
The historians' note
Sources mention Ali's standing in narration and judgement; his place is special among all Muslims.