Rashi on Exodus 18:7/רש"י על שמות י״ח:ז׳

1ויצא משה AND MOSES WENT OUT — Great honour, indeed, did Jethro receive at that moment, for as soon as Moses went out to Jethro, Aaron, Nadab and Abihu went out, and who was it that saw these go out and would not himself go out? (Midrash Tanchuma, Vayigash 7)

2וישתחו וישק לו AND HE PROSTRATED HIMSELF AND KISSED HIM — From the wording of this statement I do not know who prostrated himself to whom! But when it states in the next words: איש לרעהו, “a man to his fellow”, it becomes quite evident; for which of the two is called by the appellation איש, “man”? — This was Moses, as it is said, (Numbers 12:3) “And the man, Moses”. (Thus it was the man (איש) Moses, who bowed down to his fellow (Mekhilta).