Musar for Kiddushin 79:16

One who profanes the Name of God — profanation of the name of God is an exceedingly great sin. And what is profanation of the name of God? Rav said, "For example, if I go to a butcher and buy meat and I haven't the money to pay for it at once." The meaning of this is that if one makes light of dishonesty or robbery, then people will learn very quickly from him and will make even lighter of such a wrong (Yoma 86a). Rabbi Johanan said, "As far as I am concerned, if I walk four cubits without speaking words of the Torah or wearing Tefillin, I am guilty of profaning God's name." And the meaning of this statement is that from his example people may learn to regard these sacred things very lightly. Isaac, of the school of Rabbi Yannai said, "Profanation of God's Name is anything which causes shame to a person's companions when they hear of it, that is to say, when it is said of him that he has done unworthy deeds, people will learn from his deeds and will think, "If he can do these things, then we certainly can" — and permit themselves to commit transgressions which otherwise they would not. Rabbi Abahu said in the name of Rabbi Haninah (Kiddushin 40a), "It is better that a man should commit a transgression secretly, so that he should not profane the Name of God publicly." And the meaning of this is that other people should not learn of his bad deeds.