"There was a request for a donation," Sheen tells syndicated TV show "Entertainment Tonight" in an interview that was to air Tuesday night. "Without getting into it here ... there is a specific document relating to this that I am going to reserve for a court."
When asked if he would ever consider such a possibility, the 41-year-old actor says: "I would sooner, in exactly what I'm wearing, walk on the surface of the moon. Does that answer it?"
A spokeswoman for Richards, 36, wasn't immediately available for comment.
Sheen and Richards divorced last year. They have two daughters, 3-year-old Sam and 2-year-old Lola.
Sheen, who is nominated for an Emmy Award for his role in the CBS sitcom "Two and a Half Men," is engaged to real estate investor Brooke Mueller, 29. His screen credits include "Platoon" and the "Hot Shots!" movies.
"The thing I'm most excited about is my recent engagement," he says. "She's just easy, and loving, and smart, and if everybody was just as happy to see me when I walk through a door as her, my life would be perfect."
The interview was posted on etonline.com.