Someone once approached Rav Avrohom Pam with a question: He had somehow ended up with a significant sum of money belonging to a non-Jew. The only way to return it was by mail, and the owner would never know who had sent it. Could returning it be considered a kiddush Hashem?
Rav Pam stated that there is potential for kiddush Hashem even with hashavas aveidah that is not done in person. “The kiddush Hashem is not only the impression you make on the non-Jew,” he told his questioner. “You will make a kiddush Hashem toward your own family, who will see you acting with integrity toward non-Jews and learn from your example.”
On another occasion, a yungerman learning in kollel once realized that his bank had never cashed a check for $30,000, meant to be put toward his house. He had been on the verge of leaving kollel and the sudden windfall offered a chance to stay in learning another year. He approached Rav Pam to ask if he was permitted to keep it.
“That is not the way to remain in kollel,” the rosh yeshivah said. “You must return the money.”
To the suggestion that it might be halachically permissible to keep the money, Rav Pam replied simply that the most important thing was to be an adam shaleim (Rav Pam, by Rabbi Shimon Finkelman, p. 395).
Reproduced from Living Kiddush Hashem by Rabbi Shraga Freedman with permission of the copyright holders, ArtScroll/Mesorah Publications, Ltd.