fill-nobreak-predicate

fill-nobreak-predicate is a variable defined in `fill.el'.
Its value is

nil

• This variable may be risky if used as a file-local variable.

Documentation:
List of predicates for recognizing places not to break a line.
The predicates are called with no arguments, with point at the place to
be tested. If it returns t, fill commands do not break the line there.

You can customize this variable.