What is the ruling on the oath of one who swore, "It is forbidden, and my wife is divorced if I call so-and-so more than twenty times," while in a state of anger and uncertain about the number of times he called?

If the intent of the oath was to emphasize the frequency of contact and not a specific number, then there is no breaking of the oath if the calls were numerous, even if they did not reach the mentioned number. Similarly, there is no breaking of the oath if the swearer was overwhelmed by intense anger, losing control of his intellect.

However, if one swore, being fully aware and intending a specific number, and then it became clear that what he assumed was incorrect, the preponderant view is that there is no breaking of the oath. This falls under the category of a laghw (unintended or vain) oath, similar to someone who pronounces a divorce based on something he believes he has done, only to find out he has not.

It should be noted that the permissible oath is one sworn by Allah Almighty, not by declaring something haram (forbidden) or by divorce.