Declare an output cursor variable to the inner sp :
@c CURSOR VARYING OUTPUT
Then declare a cursor c to the select you want to return. Then open the cursor. Then set the reference:
DECLARE c CURSOR LOCAL FAST_FORWARD READ_ONLY FOR
SELECT ...
OPEN c
SET @c = c
DO NOT close or reallocate.
Now call the inner sp from the outer one supplying a cursor parameter like:
exec sp_abc a,b,c,, @cOUT OUTPUT
Once the inner sp executes, your @cOUT
is ready to fetch. Loop and then close and deallocate.