Hastamalaka was a direct disciple of Adi Shankaracharya. There is an interesting story about the life of Hastamalaka which was narrated by Adi Shankaracharya himself.
When Adi Shankara was travelling in the western parts of India he once came to Srivali Village. A worried father of a 13-year-old son, approached Adi Shankara. He told the Great Guru that the boy had been dumb from his childhood, that he had no likes and dislikes, nor a sense of honour or dishonor, and that he was completely inactive.
When Adi Shankaracharya asked the boy in a cheerful tone ‘Who Are You’, the boy, Hastamalaka, gave the famous reply which came to be known as the Hastamalaka Stotram. The boy told Adi Shankaracharya that he was Brahman through numerous examples.
After listening to the 14 verses chanted by Hastamalaka, Adi Shankaracharya realized the greatness of the boy.
He then told the father of the boy that he had become your son due to his incomplete austerities in previous birth. It is your good fortune that he was born as your son.
Adi Shankara then asked the father to allow the boy to stay with him as he will not be any use to the materialistic world.
The father was happy that his son found his true calling and left the boy with Adi Shankara.
The other disciples of Adi Shankara who witnessed the incident wanted to know how the boy attained the state of Brahman without a Guru or teaching.
Adi Shankara then told his disciples that Hastamalaka’s mother left her two-year-old child in the care of a great and highly accomplished yogi who was practicing austerities on banks of the river while she went to bathe in the river with other women. The child toddled towards the water and was drowned. Out of compassion for the disconsolate mother the yogi forsook his body and entered that of the child. That is why the boy attained self realization at a very young age.