condensed from Ein Ayah, Shabbat 9:42 Commands and Nature
[We continue with initiatives of Moshe Rabbeinu that Hashem agreed to.] Moshe separated himself from his wife. From where did he derive this? He followed the reasoning of a kal vachomer. If about Israel, who Hashem spoke to for only a short time and the time was set, still the Torah said, “They shall not get close to a woman” (Shemot 19:15), I, to whom Hashem speaks on an ongoing basis and the time for this is not set, it is all the more clear [that I should separate myself from women]. How do we know that Hashem accepted this? [It says in the Torah, “Go tell them: Return to your tents” (Devarim 5:26). And then it says: “And you (Moshe), stand here with Me” (ibid. 27). Some say that it is derived from [that which Hashem said about Moshe]: “Mouth to mouth I speak to him” (Bamidbar 12:8).