The ruling on one who swears to something based on his predominant belief

Question:
If a man swears while he predominantly believes that a certain thing has happened, but it has not actually happened, does he have to pay an expiation?

Answer:
Meaning: he swore that this thing happened?
Q: He swore that something happened, but it did not happen.
A: Meaning: he was forgetful?
Q: It was based on his predominant belief.
A: For example, "By Allah, so-and-so came," or "By Allah, so-and-so arrived," or "By Allah, the month has entered." Does he believe this?
Q: Yes.
A: The correct view is that he does not have to pay an expiation, because he believes his own statement to be true.