The Divine Image of Sri Krishna at Guruvayoor
The following story stands testimony to the antiquity and divine origin of the image of the Lord at Guruvayoor.
Long time ago, in the period Swayambhuva Manvantharam, King Suthapas, along with his spouse Prisni, desirous of begetting a child, performed penance for twelve thousand divine years before the idol of Lord Vishnu, given to them by Lord Brahma. Immensely pleased by their devotion, the Lord appeared before them in the form of Lord Vishnu and asked them to seek a desired boon. Filled with great joy on seeing the comely divine form that appeared, Suthapas prayed thrice with considerable desire: "It would be good if a son equal to Thee is born". The Lord, lover of devotees that He is, stated thus: "Only I am equal to Me. Therefore, I shall Myself incarnate as your son, in order to fulfil your desire. Since you have repeated your prayer thrice, I shall be assuming the aspect of your son in three births." Saying thus, the Lord disappeared. Not long afterwards, the Lord manifested Himself under the name,"Prisnigarbha", son of Prisni and Suthapas.
It is the same couple who were born as Kasyapa and Adithi in the next birth. They also worshipped and prayed to the same idol of the Lord as in their previous birth. Thereafter, Adithi, who was very sad at the plight of their sons, the Devas, being tormented by the Asuras, observed the austerity known as "Payovratha" (details of Payovratha are given under the commentary of Sloka 2, Dasakam 30 which deals with the Vamana Incarnation) and, as a result of that, the Lord manifested Himself as their son, Vamana.
Later, the self-same couple, in their third birth, was born as Vasudeva and Devaki in the city of Mathura. Sage Dhoumya presented them with the same idol of the Lord, which was worshipped by them in the earlier births. Owing to the force of habit or "Vasana", Devaki and Vasudeva worshipped that idol again with unstinted devotion. The Lord manifested Himself as their son, in this, their third birth also. It was to remind them of the story of the two earlier births, that the Lord manifested Himself with the insignia of Lord Vishnu when He was born as their child, Sri Krishna.
After the slaying of Kamsa, the Lord Himself installed and consecrated His own idol, the very same divine idol, which, in times gone by, was given by the Lord to Brahma, by Brahma to Prisni-Suthapas, then to Adithi-Kasyapa and then to Devaki-Vasudeva. That idol became the object of worship of all, including the Lord. Later, at the time of the Ascent of the Lord, at His own behest, the idol was recovered and reinstalled at the present location at Guruvayoor by Guru (Bruhaspati or Jupiter) and Pavana (Wind-god) for worship by those born in Kali yuga! Hantha! Bhagyam Jananaam! Fortunate indeed are those born in Kali-yuga!
This is the story narrated in the Guruvayoor Mahatmyam.