This is a famous story from Yoga Vasistha, a classic, ancient text of Hindu Advaita Vedanta meant to open the mind to speculation.
“A young boy asked his nanny to tell him a story, and the nanny told him the following story, to which the boy listened with great attention:
Once upon a time in a city which did not exist, there were three princes who were brave and happy. Of them, two were unborn and the third had not been conceived. Unfortunately, all their relatives died. The princes left their native city to go elsewhere. Very soon, unable to bear the heat of the sun, they fell into a swoon. Their feet were burnt by hot sand. The tips of grass pierced them. They reached the shade of three trees, of which two did not exist and the third had not even been planted. After resting there for some time and eating the fruits of those trees, they proceeded further.
They reached the banks of three rivers; of them two were dry and in the third there was no water. The princes had a refreshing bath and quenched their thirst in them. Then they reached a huge city which was about to be built. Entering it, they found three palaces of exceeding beauty. Of them two had not been built at all, and the third had no walls. They entered the palaces and found three golden plates; two of them had been broken in two and the third had been pulverized. They took hold of the one which had been pulverized. They took ninety-nine minus one hundred grams of rice and cooked it. They then invited three holy men to be their guests; of them two had no body and the third had no mouth. After these holy men had eaten the food, the three princes partook of the rest of the food cooked. They were greatly pleased. Thus, they lived in that city for a long, long time in peace and joy. My child, this is an extremely beautiful legend; pray remember this always, and you will grow up into a learned man. “
The Crux of the Matter: A Gentle Enquiry
You should either through yourself, or the aid of the exalted ones, be ceaselessly engaged in the pursuit of this gentle enquiry,
Who am I? What is this universe?
It is this true enquiry alone that generates Jnana (knowledge).
For more information, see: https://en.wikipedia.org/wiki/Yoga_Vasistha