Celebrated on : On the full moon day of Margashirsha
On the full moon day of Margashirsha the feast of Datta Jayanti is celebrated. In ancient times there was a very austere rishi called Atri. He was believed to be the mental son of Brahmadev, because he had been born from the splendour of Brahmadev's eyes. His wife's name was Anasuya, who was a model of conjugal fidelity.
In heaven Naradmuni used to tell the gods very interesting stories about Anasuya's fidelity to her husband. This provoked the jealousy of Sarasvati, Laxmi, and Parvati, who decided to lower Anasuya's reputation. They sent Brahma, Vishnu and Mahesh (Shankar or Shiva) to earth for the purpose of bringing about her disgrace.
Brahma, Vishnu and Mahesh became three guests, and seeing that Atri was not in his house, they knocked at the door. Anasuya at once welcomed the guests. She got food ready for them and requested them to have a meal. Then they said that they would eat only on one condition. The strange condition was that Anasuya should serve them the food without any clothes on.
The Three Babies
Anasuya was dumbfounded. But in a trice she thought of a solution, and by the power of her mind she turned the three guests into small babies. The babies began to cry. She kept them in a cradle and with great love she began to rock them.
There was a commotion in heaven. The three wives of the gods. Sarasvati, Laxmi and Parvati became distressed. "If the three great gods become small babies, who will take the responsibility of the universe?"
Brahma, Vishnu, and Mahesh were sorry and asked for Anasuya's forgiveness. The form of three babies kept a particle of their being in the house of that faithful wife and they returned to heaven.
Anasuya named the three babies, Som, Datta, and Durvas. When they grew up Som went to the moon, and Durvas went to the jungle to do penance. Before leaving both of them kept their particle of being with Datta. Thus Datta became the combined avatar of Brahma, Vishnu and Mahesh.
Datta being the mental son of Anasuya, he was also the mental son of Atri, and therefore his name became Dattatreya.
Dattatreya learned the Vedas and then began to teach them. Anasuya wanted him to get married. But Dattatreya was pleased with the celibate state. So after instructing her on Brahmavidya (doctrine of Brahma) he obtained her permission and left home.
'Shri Guru Charitra'