Story of Chyavana Muni, Sukanya is mentioned in several Puranas.. The story of Chyavana Muni and Sukanya goes like this..
Vaivaswata Manu’s another son Saryati gave birth to Sukanya. The latter when she came of age visited a forest once along with her companions and playfully prierced into a bush while amused about what she thought were glowing worms. But they were actually the eyes of a Muni named Chyavana performing Tapas with eyes wide open and in the process got blinded. The girl got confused when blood oozed out from the bush and ran away.
The blinded Muni realised that a young princess did the indiscretion and gave a Shaap that the entire military force of the King should suffer with stoppage of their excretions. Meanwhile Sukanya conveyed to the King of her playful rashness and of the Muni’s shaap. King Saryati along with Sukanya approached the Muni and prostrated to him seeking unreserved pardon; the King offered the young Sukanya to wed the old Muni so that she could serve the Muni in his blindness.
In course of time, Sukanya got used to family life serving the blind Muni in his daily puja and other chores. She excelled herself in her ‘Pativratya’ or undisputed devotion to her husband.
One day, the two Ashvini Kumars who were the Physicians of Devas passed by the Ashram of Chyavana Muni and were highly impressed with the selfless and ideal service being performed by Sukanya as an example of Pativratya. They cured the Muni’s blindness and the grateful Chyavana offered a boon to the Ashvini Kumars. The latter desired that they would like to have access to ‘Amrit’which was provided to Devas but was denied to them. Chyavana Muni made a request to Indra but he refused.
The Muni took up this as an insult to him and performed an elaborate Yagna an favour of Brahma Deva and the latter who was pleased by the Muni’s Yagna instructed Ashvini Kumars to accord the same status to Devas and thus have access to the drink of Amrita eversince.