Rashi on Exodus 4:18/רש"י על שמות ד׳:י״ח

1וישב אל יתר חתנו AND HE RETURNED TO JETHRO HIS FATHER-IN-LAW, to obtain his permission to go to Egypt, for he had sworn to him that he would not leave Midian except by his permission (Nedarim 65a). He is here called יתר and he had seven names: Reuel, Jether, Jethro, Keni, Hobab, Cheber and Putiel (cf. Mekhilta)