Once, the demon Hayagriva stole the Vedas from Lord Brahma, leading to widespread chaos and 
unrighteousness in the universe. To restore order and righteousness, Lord Vishnu incarnated as Matsya (a divine fish) and defeated Hayagriva, retrieving the sacred Vedas. This first incarnation of Lord Vishnu took place on the Tritiya Tithi (third day) of the Shukla Paksha in the month of Chaitra.
King Satyavrata and the Divine Fish
Before the great deluge (Pralaya), there was a pious and virtuous king named Satyavrata. One day, while performing rituals in the Kritamala River, he scooped water in his hands for offering, only to find a tiny fish in his palm. As he attempted to release it back into the river, the fish spoke to him, saying, “O King, please protect me! The larger creatures in the water may devour me.”
Moved by compassion, the king placed the fish in his water-filled kamandalu (sacred pitcher). However, overnight, the fish grew so large that the kamandalu became too small to contain it. Astonished, the king transferred it to a larger vessel, then to a pond, a river, and finally to the ocean. But the fish kept growing at an incredible pace.
Realizing this was no ordinary fish, Satyavrata asked in wonder, “Who are you? Your size is beyond natural growth. You must be the Supreme Lord.”
The divine fish then revealed its true identity, saying, “I am Lord Vishnu. The demon Hayagriva has stolen the Vedas, leading to the spread of ignorance and sin. I will slay him and restore the Vedas. Seven days from now, a great flood will submerge the earth. At that time, a boat will arrive for you. Gather the seven great sages (Saptarishis) along with seeds of all crops and medicinal herbs, and board the boat. I will return to guide you and impart the knowledge of the Self (Atma-Tattva).”
The Great Deluge and the Divine Rescue
As predicted, seven days later, the great flood began engulfing the earth. Lord Vishnu, in His Matsya form, reappeared and secured the boat to His horn using the serpent Vasuki as a rope. He guided King Satyavrata, the Saptarishis, and the life-preserving seeds to the safety of the Himalayas.
During the voyage, Lord Vishnu imparted the profound knowledge of the Self, saying, “I reside in all beings. There is no high or low; all creatures are equal. The world is transient, and beyond this fleeting existence, only I am eternal. One who realizes My presence in everything transcends the cycle of birth and death and attains liberation.”
The Defeat of Hayagriva and the Restoration of the Vedas
After the flood subsided, Matsya Vishnu confronted and vanquished the demon Hayagriva, reclaiming the stolen Vedas. He then returned them to Lord Brahma, ensuring the restoration of divine wisdom in the universe.
Through His Matsya Avatar, Lord Vishnu not only saved the sacred scriptures but also enlightened King Satyavrata, who attained liberation from the cycle of birth and death. Thus, the first incarnation of Lord Vishnu established the eternal truth of righteousness, divine wisdom, and universal equality.