Hastamalaka

Here he was to get one more great disciple. Prabhakara was a brahmin.
He had a son who was a dumb boy. He appeared to be dull. But Shankara
felt that he was a yogi. Instead of asking the parents who had brought
the boy ‘Why is the boy like this? since when?’ he asked the boy
straightaway : “Who are you, my boy?” What else could be so sacred a
place as the one where the divine master was standing for the yogi to
break his silence? One who was dumb spoke in answer, “I am the eternal
self and not dead matter.” This was the simplest form of expressing the
nature of the self. By the grace of the master, the dull and the silent son
of that couple revealed himself to be a great and wise sage. The master
felt happy and taking him as disciple, named him Hastamalaka.

From freeindia.org

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