In the chapter 28, Section 3 of Satarudra Samhita of Shiva Purana, the story of incarnation of Shiva as Yatinatha Hamsa (Swan) is mentioned.
On the mountain Arbuda (mount Abu) there lived a hunter Ahuka of Bhilla tribe. His wife observed some good rites. Both of them were great devotees of Shiva and worshipped Shiva. Once, this Bhilla went far into the forest for fetching food for his wife.
In the meantime towards the evening, Shiva assumed the guise of an ascetic and came to his house to test him. Ahuka came back then and lovingly worshipped the leading ascetic. In order to test his feelings, Shiva in the guise of an ascetic, indulging in great sports lovingly said to him in a piteous tone.
“O Bhilla, give me some place here to stay today. I shall by all means leave in the next morning; you will be blessed for ever.”
“O lord, what you say is true. But please listen to me. The room is not spacious enough to hold us all together.”
The ascetic wanted to leave. By that time, considering the trend of thought of her husband the Bhilla’s wife said: “O lord, give him room to stay. Do not turn out a guest. Consider the duty of a householder or virtue will be affected. You stay in the house along with the ascetic. I shall remain outside with immense weapons.”
On hearing the virtuous and auspicious words of his wife, the Bhilla thought thus. “How can I stay in the house after keeping my wife out? It will be sinful on my part if the ascetic goes elsewhere. Neither of the two courses is proper for a householder. What is destined to happen will surely happen. I shall stay outside.”
After thinking thus and insisting on it, he kept both of them within the house joyously, he stayed outside the house keeping all the weapons beside him. During the night the cruel beasts of prey tormented him. He too strenuously withstood them to the extent of his ability.
Thus fighting strenuously and although very strong, the Bhilla was devoured by the beasts of prey which seized him forcibly, as though indeed by his own adverse fate.
Getting up in the morning the ascetic saw the Bhilla of the forest devoured by the beasts of prey. He felt much dejected at it. Although the Bhilla’s wife too was distressed, she suppressed her sorrow on seeing the ascetic miserable and spoke thus.
She said: — “O ascetic, why are you sorry? What has happened is for good. Blessed and contented is he since the death has happened in this manner. O ascetic, reducing myself to ashes, I too shall follow him. Be pleased to arrange for the pyre. This is the eternal duty of women. On hearing her words which he thought to be proper, the ascetic arranged the pyre. She entered the pyre dutifully. In the meantime Shiva himself appeared before her and spoke praising her lovingly “O blessed lady, O blessed lady.”
Shiva said: — “O sinless lady, mention the boon you wish to have. I am pleased with your conduct. There is nothing which cannot be granted to you. I am utterly subservient to you.”
On hearing the words of Shiva yielding the greatest bliss she felt the highest pleasure. She did not remember anything. On seeing her in that state, Shiva was much delighted. He asked her again to mention the boon she wished to have.
Shiva said: — “This ascetic who is in my own form will assume the form of a swan in the next birth. He will lovingly unite both of you. This Bhilla will be born as Nala, the son of Virasena, in the excellent city of Niṣadha. There is no doubt in this. You will be born in the illustrious city of Vidarbha as the daughter of king Bhima. You will be famous as Damayanti endowed with all good qualities. After coming together you will enjoy royal pleasures. You will attain salvation too, inaccessible even to leading Yogins.”
After saying this, Shiva assumed the form of phallic image. He became stationary. He is thereafter remembered as Acalesha.
The Bhilla Ahuka was born as the son of Virasena in the city of Niṣadha. He was the great king Nala. Wife of Ahuka was born as the daughter of king Bhima in the city of Vidarbha. She became famous as Damayanti.
Shiva in the form of Yatinatha was born as a swan. He managed the marriage of Damayanti with Nala. It was due to the merit accruing from hospitality that lord Shiva gave them pleasure after assuming the form of a swan. The incarnation of Shiva as the swan adept in the art of intelligence, was the bestower of great bliss to Damayanti as well as to Nala.