Wat Pournima is a women's festival celebrated in the month of Jesht (May-June). On this day married women observe a fast and tie threads around a banyan tree and pray for the same husband in every birth.
The legend behind the banyan tree is the story of Satyavan
and Savitri. The story goes that Satyavan and Savitri were married. It had
been foretold that Satyavan would die early. One day, Satyavan, after
spending the morning cutting firewood, felt tired and lay his head down on
Savitri's lap under a banyan tree. Savitri knew that the predicted end was
near and waited fearfully for one of the messengers of Yama, the god of
death. When the messenger came, Savitri refused to give up her husband and
sent him packing. Messenger after messenger tried to take Satyavan away,
but in vain.
Finally, Yama himself appeared before her. Since she was still adamant, he offered her a boon. She asked for the well being of her in-laws. He granted it to her. She then followed him as he took Satyavan's body away. He offered her another boon. She now asked for the well being of her parents. This boon, too, was granted. But she was relentless, and continued to follow him. As they approached Yama's abode, he offered her a final boon. She asked for a son. He granted it. She then asked him how it would be possible for her to beget sons without her husband. Yama was trapped and had to return her husband.
On the strength of this legend, married women pray to the banyan tree for the long life of their husbands and for children Their fast is observed right through the night till the next morning.