From: Rabbi Moshe Sofer
To: Rabbi David
A community sought to sell sefarim bequeathed for public Torah study in order to fund mikvah construction. The Chasam Sofer emphatically forbids this, ruling that Talmud Torah outranks mikvah as a mitzvah, and since the donor's name has not been forgotten from the books, redirecting them to a lesser mitzvah—especially one that would eliminate the original purpose entirely—is impermissible. He concludes that the community must find alternative funding for the mikvah.
Source: Shu"t Chasam Sofer YD §244