And he said. It is suspected that the true reading here is, "and they said,"—i.e; some one said—"to Moses, behold thy father-in-law" (or "brother-in-law"), "Jethro, is come unto thee." So the LXX; and many moderns, as Kennicott, Geddes, Boothroyd, Canon Cook, and others.
But the explanation, that Jethro, on arriving in the vicinity of Moses, sent a messenger to him, who spoke in his name (Rosenmuller, Patrick, Pool, Kalisch, Keil, etc.) is at any rate plausible, and removes all necessity of altering the text.