The smallest ABS size is 1-1/2"
You can use a Mission Coupling, CK115,
1-1/2" CI, PL or ST to 1-1/2" COPPER or 1-1/4" PL
Is it possible to connect PVC to abs for a vent using threaded connections or transition glue. This would only be done in the horizontal section of the.vent 6" above a standpipe. I can not find 1.25" abs pipe.