From: Rabbi Moshe Sofer
To: Rabbi Hirsch Leviass
The question is whether the Torah obligation to return a lost object overrides the rabbinic prohibition of handling muktzeh on Shabbos. The Chasam Sofer distinguishes: where the Sages already permit handling one's own property, returning a found object is likewise permitted, but where handling even one's own property remains prohibited, the Sages uphold their decree.
Source: Shu"t Chasam Sofer OC §82