Will a son be considered to have broken an oath if his mother swore that he would not open WhatsApp, but he read the messages from outside without entering the application, or he entered by mistake and exited immediately?

The reference point for oaths is the intention of the swearer. If there is no intention, then the reference point is the reason for the oath. If both intention and reason are absent, then the reference point is the specific designation. If all of these are absent, then the reference point is what the name encompasses (first legal, then customary, then linguistic).

So, if the swearer did not intend anything, one refers to the reason for the oath. If the reason necessitates not looking at notifications, then looking at them is considered breaking the oath. If the reason is absent, then it appears that merely reading notifications on the device screen is not considered opening the application, and thus does not break the oath.

However, if the application was entered by mistake and exited immediately, then, according to the preponderant opinion, the son's action of doing what was sworn against, whether forgetfully or by mistake, does not make the mother break her oath.