In this excerpt from the Brahma Purana, the sage Vyasa describes the various incarnations of Vishnu. After summarizing the story of the Ramayana, he says this:
The people who are conversant with ancient legends sing the following popular folk song thus - "People had a close and real bond of love with Rama. The intelligent lord had greatness. He was a young man with red eyes and refulgent face. He spoke with limitation and restraint. His arms extended upto his knees. He had a gentle face. He had great arms and leonine shoulders. He ruled over the earth for ten thousand years. There were the following sounds continuously in his kingdom - the sound of the chanting of Riks, Saman and Yajus Mantras; the twanging sound of the bow. This sound never ceased viz. "Let this be given, let this be eaten." Rama the son of Dasharatha richly possessed Sattva attributes and other qualities. He shone with his own brilliance, more brilliantly than the moon and the sun. He performed hundreds of holy sacrifices at the conclusion of which excellent gifts were offered to the Brahmins. He of great strength left Ayodhya and went to heaven. It was in this manner that the lord of great arms, the scion of the family of Ikshvaku killed Ravana along with his attendants and went of to heaven."
My question is, what is this "popular folk song" quoted by Vyasa? Vyasa composed the Puranas near the end of the Dwapara Yuga or the beginning of the Kali Yuga, and yet even he says that this song is sung by "the people who are conversant with ancient legends". So that would make it an extremely ancient folk song.
Does anyone know how old it is? Are there any other scriptures, for instance other Puranas, that refer to this folk song?