Elizabeth asks John to go to Abigail and prove to her that their relationship is truly over.
Here is the scene, from Act 2:
Elizabeth: ...Would you favor me with this? Go to Abigail.
Proctor (his soul hardening as he senses): What have I to say to Abigail?
Elizabeth (delicately): John-- grant me this. You have a faulty understanding of young girls. There is a promise made in any bed --
Proctor: (Striving against his anger): What promise!
Elizabeth: Spoke or silent, a promise is surely made. And she may dot on it now -- I am sure she does -- and thinks to kill me, then to take my place.
Proctor: When will you know me, woman? Were I stone I would have cracked for shame this seven month!
Elizabeth: Then go to her and tell her she's a whore. Whatever promise she may sense -- break it, John, break it.