Babylonian Talmud Shabbat 146b
Mishnah: One whose clothes get wet from water on the road may continue walking in them without concern [of violating Shabbat]. When he arrives at his courtyard he may lay them in the sun [to dry] but not in front of [other] people.
Talmud: Rav Yehuda reported, "Rav said, 'Anytime that the Sages made a prohibition because of marit ayin (for the sake of appearance) it applies even in the most private of settings.'"
There is another type of prohibition that applies not only to the rules of Shabbat, but to all other areas of Jewish living as well. Marit ayin—literally in sight of eye—is a principle that demands not only that our actions accord with what is right, but that the appearance of all those actions be above suspicion. The Mishnah, in tractate Sheqalim (3:2), explains, "One must fulfill human expectations, just as one does Divine." Our Sages understood that religious communities are human communities. We believe that living in a human community requires that we take other people's needs and concerns into account.
In the above passage, our mishnah explains, though one need not worry that walking in the rain or fording a body of water is prohibited on Shabbat (a prohibition that could be suggested by the similarity to laundering clothes), nonetheless, on arriving home, one must not hang those clothes up to dry in plain sight. Those who see wet clothes hanging to dry might think that the owner of the clothes laundered them on Shabbat. Rav Yehuda takes this prohibition one step further. Based on earlier authorities he demands that we not perform acts prohibited because of marit ayin even in private. He seems to believe that all of our actions, public and private should be in consonance. May we all strive for this high level of integrity in days to come.