find-function-library

find-function-library is a compiled Lisp function in `find-func.el'.

(find-function-library FUNCTION &optional LISP-ONLY VERBOSE)

Return the library FUNCTION is defined in.

If FUNCTION is a built-in function and LISP-ONLY is non-nil,
signal an error.

If VERBOSE is non-nil, and FUNCTION is an alias, display a
message about the whole chain of aliases.