Does divorce occur if the wife's sister's son calls from his mother's (the sister's) phone, even though the husband swore that his wife would be divorced if her sister called her or if she called her sister?

Conditional divorce is a matter of disagreement among jurists. The majority of them believe that divorce occurs when the condition is met.

However, others, including Sheikh al-Islam Ibn Taymiyyah (whose view is adopted on this website), hold that the ruling depends on the intention of the one who made the oath. If he intended merely to prevent or encourage something and did not intend to effect a divorce, then its ruling is that of an oath (yamin), and an expiation for breaking an oath (kaffarat yamin) is required upon breach, and no divorce occurs. But if he intended to effect a divorce, then it occurs when the condition is met.

Based on this in the present matter, if the intention was merely to deter the wife from communicating with her sister, then upon the fulfillment of the condition, an expiation for an oath is required. However, if the intention was to effect a divorce, then it occurs as soon as communication takes place.

Nevertheless, the call made by her sister's son has no consequence, because the caller was the sister's son, not the sister herself, and because the wife did not answer the call.

It should be noted that maintaining kinship ties (silat al-arham) is obligatory, and the husband should be an aid to his wife in this regard.