What is the liability when a man accuses another man by saying, 'O adulterer, son of an adulterer'?

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If a man says to another man, 'O adulterer, son of an adulterer' (Ya zani ibn al-zani), two punishments for slander (haddan) are incumbent upon the accuser. Mak'hul is cited as holding this opinion, and Imam Ahmad affirmed it when questioned.