Exodus 17:10

AND MOSES AND AARON AND HUR — From this we may infer as regards a public fast that three men must pass before the Holy Ark (i. e. must officiate at prayer) — we may infer this because they (the Israelites) were then engaged in fasting (Mekhilta). חור HUR was the son of Miriam and her husband was Caleb (Sotah 11b).

וַיַּ֣עַשׂ יְהוֹשֻׁ֗עַ כַּאֲשֶׁ֤ר אָֽמַר־לוֹ֙ מֹשֶׁ֔ה לְהִלָּחֵ֖ם בַּעֲמָלֵ֑ק וּמֹשֶׁה֙ אַהֲרֹ֣ן וְח֔וּר עָל֖וּ רֹ֥אשׁ הַגִּבְעָֽה׃

So Yehoshua did as Moshe had said to him, and fought with ῾Amaleq: and Moshe, Aharon and Ḥur went up to the top of the hill.