Swan

Lord Siva disguised as a Yatinath to test the depth of devotion by a Bhil couple named Ahuk and Ahuka and sought resting place overnight but even while Ahuk said that their hut was just enough for two persons, Ahuka agreed to sleep outside to let the guest sleep inside the hut, while a wild animal killed Ahuk yet Ahuka quietly tried to jump in the husband’s funeral pyre when Lord Siva manifested and blessed that the couple to become Nala and Damayanti in the next birth as the Lord would appear as a ‘Hamsa’ (Swan) to unite them

1. http://paninformation.blogspot.com/search/label/NalopakhyanaParva
2. https://www.google.com/search?q=Yatinath