Connecting a P-trap to a female drain connector in the wall
A 1 1/4" female FIP adapter worked perfectly. As soon as I saw it, I was embarassed for not having thought of it earlier. 



I used some teflon tape, screwed the FIP adapter onto the adapter coming out of the wall, then just glued my 1 1/4" pipe directly into it. No reduction in pipe sizes, and 100% ABS parts.