The great sage Ayodhyaumya had many disciples, but a young boy called Upamanyu was his favourite. One day, the sage decided to test Upmanyu's devotion and asked him, "You look very healthy, what do you eat?" In those days, sages and their disciples used to beg for food and alms. Upmanyu calmly replied, "I eat the food that I get by begging. " On hearing this, The sage instructed Upmanyu not to consume any food that he received as alms without asking for his permission first. Upmanyu was very obedient and from the next day itself, he offered everything that he received to the sage. The sage took away all the food and gave nothing to Upmanyu.
After a few days, the sage noticed that Upmanyu still looked very healthy. The sage then asked him, "I take away all the food that you get, so what do you eat?" Upmanyu explained that he offered the sage everything, and that he ate what he got the second time he went begging. The sage scolded Upmanyu and ordered, "You shouldn't beg twice, because then there will be nothing left for other students. you should not be greedy. " Upmanyu obediently followed what his teacher said.
After some days, the saint noticed that Upmanyu still looked hale and hearty and asked him, you still look healthy, what do you eat these days?" Upmanyu replied saying, "when I take the cows out to graze, I drink some of the milk that they give. " The sage immediately forbade Upmanyu from having milk from the cows. As usual, Upmanyu followed his teacher's instructions.
However Upmanyu's health still did not suffer. The sage approached him again after a few days and asked him what he ate. Upamanyu promptly replied that he ate the foam that the calves produced after having milk from the cows. The sage told Upmanyu that this would affect the health of the calves and he should not do so. Upmanyu followed Ayodhdhaymya's advice.
The next day, when Upmanyu took the cows for grazing as usual, he felt very hungry. When he couldn't control his hunger anymore, he ate the leaves of a plant called Aak. The leaves of this plant were very poisonous and Upmanyu became blind. He kept wandering in the forest and then fell into a dry well. When Upamanyu did not return in the evening, the sage was worried and went with disciples to look for Upmanyu. They found Upmanyu in the well and pulled him out. When the sage heard how Upmanyu had been blinded, he asked him to pray to the Ashwin Kumars, the doctors of the gods, and request them to restore his eyesight. Soon, the Ashwini Kumars appeared and gave Upmanyu a medicine. and said that he would not eat anything without Ayodhdhaumya's permission. The Ashwini Kumars tried their best to convince Upmanyu to have the medicine but Upmanyu said that he would rather stay blind forever than disobey the orders of the sage.
The gods were impressed by Upmanyu's love, respect, and devotion for his teacher and blessed him. They restored his eyesight. Ayodhdhaumya was also very pleased with Upamanyu and told him that he had passed the test. The sage blessed Upmanyu and gave him a boon that he wouldn't need to learn religious texts but would know them automatically.