When Karṇa attained manhood he approached Droṇa in order to learn the secrets of the brahmāstra. Droṇa replied, however, that the knowledge he desired should only be given to a qualified Brahmin who had practiced vows, or to an accomplished kṣatriya who had undergone penance. “O Radheya, you are neither. Indeed, you hail from the suta class of śūdras. I will not instruct you.”
Burning with anger, Karṇa bowed before Droṇa and left for the Mahendra mountain, where he knew he would find Paraśurāma. When he found the sage, Karṇa bowed at his feet and said, “I am a Brahmin from Bhṛgu’s race. Kindly instruct me in weaponry. I desire to know the brahmāstra.”
Paraśurāma received him kindly and agreed to teach him. Karṇa then lived at the sage’s ashram and learned many types of warfare and weaponry from him. While residing on the heavenly mountain, he became a favorite of the many Siddhas and Gandharvas who sported there. He would often go about with his bow and sword, hunting game and the wild beasts.
Once, while hunting, he accidentally slew a Brahmin’s cow. Distraught, he went at once to the Brahmin and told him what had happened. Dropping to the ground before the sage, he said in a tearful voice, “O best of men, I have killed your cow quite against my will and desire. Forgive me! Please allow me to make some recompense.”
But the Brahmin, seeing his beloved cow lying dead, was filled with anger. His face turned red and he took hold of his sacred thread, signifying his intention to curse Karṇa. “O wicked one, you deserve death for this crime. You will suffer the fruit of your foolishness even in this life. When you finally meet in battle with your mortal enemy, your chariot will be swallowed by the earth. As you have carelessly cut down my cow, so will your head be cut off by your foe. Go now, O vile man!”
Karṇa tried to appease the Brahmin, but he would not relent. “My words will not prove false,” he replied. Finally Karṇa went away, hanging his head in sorrow.
Karṇa remained in Paraśurāma’s ashram for some time, pleasing the sage by his aptitude for learning and by his humble service attitude. Paraśurāma taught him everything about the Brahmā weapon, as well as other powerful missiles, such as the mighty Bhārgava astra.
One day, the sage took a walk in the woods, taking Karṇa with him. After some time, he became tired and lay down to rest on a grassy slope, placing his head on Karṇa’s lap. As the ṛṣi slept, a large insect crawled onto Karṇa’s leg and began to burrow into his flesh. Digging deeply, the insect drank Karṇa’s blood. Not wanting to disturb his guru, Karṇa did not move. He sat without showing the least sign of pain.
After some minutes his warm blood ran onto Paraśurāma’s face and awakened him. When he saw the eight-legged insect on Karṇa’s leg, he melted it with his glance. A Rākṣasa suddenly rose into the sky and addressed Paraśurāma with folded palms. “O best of ascetics, you have saved me from a hellish existence. Formerly I lived in the higher planets, but one day I assaulted Bhṛgu’s wife, who cursed me to become an insect. When I begged for mercy, he told me I would be released from the curse when I came in contact with Rāma, the son of Jamadagni. You have rescued me. Thank you, O sage. I will now depart.”
The Rākṣasa vanished, leaving the ṛṣi glaring at Karṇa. “O wretch!” he exclaimed. “How can you be a Brahmin? No Brahmin could tolerate such pain. Only a kṣatriya has such patience. Tell me the truth--who are you?”
Trembling, Karṇa replied, “O lord, I am Karṇa and I have been born in the suta race, a mixture of Brahmins and kṣatriyas. Coming to you as my teacher, O scion of Bhṛgu’s line, I saw you as my father. Thus did I call myself a member of Bhṛgu’s family. Forgive me, for I am your humble servant.”
Paraśurāma smiled through his anger. Looking down at Karṇa, who had prostrated himself on the earth with folded palms, the sage said, “Greedy for weapons, you have lied to me. Therefore, I say this: When you face your greatest danger and desperately need your most powerful celestial weapon, you will not be able to remember the mantras. Otherwise, you will be peerless in weaponry. Now leave at once, for this is no place for one who behaves falsely.”
Karṇa went shamefacedly away and later joined Duryodhana in Hastināpura.