Honoré de Balzac 
The Atheist’s Mass [PDF ebook] 

La Messe de l’athée (English ‘The Atheist’s Mass’) is a short story by Honoré de Balzac, published in 1836. It one of the Scènes de la vie privée in La Comédie humaine.
The main character, Desplein is a successful surgeon and an atheist. His former assistant and friend is Doctor Horace Bianchon. One day Bianchon sees Desplein going into the Saint-Sulpice church, and follows him. He sees Desplein alone attending a mass. After Desplein departs, Bianchon questions the priest and finds that Desplein attends a mass at the church four times a year which he himself pays for.
A few years later, Bianchon again sees Desplein going into Saint-Sulpice for the regular mass. This time he questions Desplein about it. Desplein explains that the mass is in memory of a friend of his, a water carrier named Bourgeat. When Desplein was a poor medical student, Bourgeat was his neighbour in the same building. The landlord evicted both of them on the same day. They agreed to look for a new place together. They eventually found two cheap rooms in the attic of another building. From then on, Bourgeat became a father figure to Desplein. He helped to pay for Desplein’s education, and did menial tasks like cutting the wood. After Desplein became successful, he bought Bourgeat a horse and cart for his water carrying work.
After Bourgeat’s death, and knowing that Bourgeat was a devout Catholic, Desplein decided to have four masses a year for Bourgeat at Saint-Sulpice church.