Rashi on Exodus 18:6/רש"י על שמות י״ח:ו׳

1ויאמר אל משה AND HE SAID UNTO MOSES through a messenger (Mekhilta).

2אני חתנך יתרו וגו I, THY FATHER-IN-LAW, JETHRO etc. — If you will not come out for my own sake, come out for the sake of your wife; and if you will not come out for your wife’s sake, come out for the sake of your two sons (Mekhilta).