There's a reference to Jethro in the Midrash Rabbah which overlaps some of what is said about him in the Quran. (It's not always easy to find things in Midrash-writings; the reference "2:16" is one way of listing it; another is "Exodus (Shemoth) 1:32," or, using the Soncino edition, Vol. III, page 40.) Here's the pertinent selection:

"The fact is, say the Sages, that Jethro was at first a priest to idolatrous worship, but when he saw that there was no truth to it, he despised it and thought of repenting even before Moses came. He summoned his townspeople and said, "Hitherto I ministered unto you, but now I have become old, choose another priest." And he returned unto them all the insignia of his priesthood. Whereupon they excommunicated him, that no man be in his company, or work for him or tend his flock; he asked the shepherds to look after his flock, but they refused, and he had to employ his daughters." (from p. 40, Midrash Rabbah, Vol. III, translated by S.M. Lehrman, (C) 1983 The Soncino Press, NY.)

If one removes the formulaic sentences from the section about Shuaib in 7:85-93, and the parts that say that his people were punished, and the parts invented to create parallels with Muhammad, there's not much left, but what /is/ left bears a fair resemblance to the account in Midrash Rabbah.

Yours in Christ,

Waterrock