Story of Vasthu Purusha in the MATSYA PURANA

Once in Vedic period there lived a demon called Andhakasura, who killed sages and seers. Lord Shiva had to fight with demon to protect the world and killed him after a long war which had continued for years. While fighting with the demon, the Lord Shiva was very much tired and began to sweat profusely. When the sweat fell down on the earth, a child was born of the drops of Shiva's sweat.