The Chofetz Chaim once traveled to another city, and the people of the city emerged to greet the Gadol Hador. Many wealthy men of the city were among those who came to greet the Chofetz Chaim and receive a bracha.
One wealthy man approached the Chofetz Chaim and gave him a sizable donation for Yeshivas Radin. The Chofetz Chaim grabbed the man's hand and began to cry bitterly, saying, "This hand gives tzedaka with such respect, and alas it is michalel the Shabbos." The Chofetz Chaim continued to hold the man's hand and cry, and the wealthy man's heart melted, and he too began crying bitterly.
The wealthy man said, "Rebbe, I promise you that from today I will keep the Shabbos. But please allow me to be able to perform melacha this coming Shabbos at least, so I can wrap up my affairs."
The Chofetz Chaim answered with great emotion, "My dear son, if it was my Shabbos I would be mochel you and allow you whatever you request, but it's the Shabbos of Hakadosh Boruch Hu, the King of Kings. I can't allow even one moment of chilul Shabbos!
The wealthy man accepted the words of the Chofetz Chaim, and began keeping the Shabbos from that week, and eventually became fully observant. (Ukarasa Leshabbos Oneg)