מדרש על שמות 18:5

(Exod. 18:5–6:) NOW JETHRO, MOSES' FATHER-IN-LAW CAME…. AND HE SAID UNTO MOSES: I AM YOUR FATHER-IN-LAW…. Who said to Moses: I AM YOUR FATHER-IN-LAW? He was unable to come to Moses. What did he do? He wrote a letter and tied it on an arrow. Then he shot, and the arrow came to Moses. Moses read it and went out to him, as stated (in vs. 7): SO MOSES WENT OUT TO MEET JETHRO. He entered the camp along with him. What is written (in vs. 12)? AND AARON CAME WITH ALL THE ELDERS OF ISRAEL TO EAT BREAD <BEFORE THE LORD WITH MOSES' FATHER-IN-LAW >. When they had eaten with him, he said: Give me permission to go to my <own> place. Moses said to him (in Numb. 10:32): IT SHALL BE THAT, IF YOU COME WITH US, IT SHALL COME TO PASS THAT WHATEVER GOOD THE LORD DOES FOR US WE WILL DO FOR YOU. <Jethro> said to him: I want to go and utter the Holy One's praise in my own place. Immediately (in Exod. 18:27): MOSES SENT HIS FATHER-IN-LAW AWAY…. Now when the Holy One does miracles for Israel, they praise him [and the nations of the world praise him]. Thus it is stated (in Ps. 138:4): {THESE PEOPLES} ALL THE KINGS OF THE EARTH SHALL GIVE THANKS TO YOU, [O LORD,] FOR THEY HAVE HEARD THE WORDS OF YOUR MOUTH.