What is the source of the story about the melted gold in the destroyed temple in 70 AD?

In Matthew 24:2, Mark 13:2 and Luke 21:6, Jesus seems to indicate that in the coming temple destruction, "not one stone will be left upon another". And, indeed, this seems to be the case from the current ruins. However, I have come across several commentaries that state that because the temple was burned, the gold that was on the walls, melted and ran between the stones, as well as into them. The Roman solders then took stone from stone in a effort to retrieve the gold, thus giving literal fulfillment of Jesus' prophecy. Having encountered this explanation several times in the course of my studies, I wanted to find the source for this story, but, as of this date, am unable to do so. I don't find anything in Josephus relating to that gold-seeking activity. Does anyone know of a source document or documents that can authenticate this story?