I am working on a Bible study for Ephesians and I've noticed in numerous places that people allude to a statement from the Mishnah that Jews thought Gentiles' purpose was to be fuel for the fires of hell, but I have yet to see a source actually cite where that comes from. Anyone know about this?

My intuition is that everyone is just grabbing it from Barclay's works. But I'd rather do my own work. So far though I haven't found any proper attribution.