Shilad did a tremendous penance to please Lord Shiva. His penance continued for thousands of year. At last, Lord Shiva appeared before him and said–“I am extremely pleased by you devotion. I shall bless you with a son who will become famous for his knowledge and learning.” But, Shilad was desirous of a self-born and immortal son. Lord Shiva said–‘Your desire will be fulfilled. Even Lord Brahma had requested me to take an incarnation. I will take birth as your son and my name will be Nandi.”
In course of time, Shiva manifested from the oblation site. The deities became pleased after seeing Nandi, who possessed three eyes, four arms and a crown on his head.