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One example comes from the Khemaka Sutta:
That is what Ven. Khemaka said. Gratified, the elder monks delighted in his words. And while this explanation was being given, the minds of sixty-some monks, through no clinging, were fully released from fermentations β as was Ven. Khemaka's.
Before he taught them, Ven. Khemaka was not an arahant. But after he taught them, both he and his audience became arahants.