The ruling on one who swore to divorce his wife to prevent her from speaking to her sister, and she spoke to her

Question:
May Allah reward you with good. He says: I swore to divorce my wife if she speaks to her sister. This was during her post-natal bleeding, in the days following the birth, and she had not yet become ritually pure. Then she spoke to her after she had become pure, and I learned of it from her. Is there an expiation for this oath upon me? May Allah reward you with good.

Answer:
If you intended the divorce, meaning you intended to make the divorce contingent on her speaking to her, then the divorce takes place when she speaks to her. One of your divorces is lost, and you have two remaining, unless there was a previous divorce that would complete the three, in which case she is divorced.
She is divorced with a major final separation. However, if you intended by that to prevent her from speaking, and did not intend to divorce her, but only intended to prevent her from speaking, then this is considered an oath according to the correct opinion. It is considered one of the oaths that entails an expiation, due to the saying of Allah the Exalted: meaning the expiation. This is an oath that is followed by its release through the expiation. So upon you is the expiation of an oath according to the correct opinion of the scholars' two opinions. It is the freeing of a slave. If you do not find one, it is the feeding of ten poor people, or the clothing of ten poor people, with the choice between these matters. If you do not find any of them, it is obligatory for you to fast three days. Yes.