She believed him first

He came back from the cave shaking, and what he said when he reached the house was: cover me, cover me.

So she covered him, and waited until the fear had gone out of him. Then he told her what had happened and said that he feared for himself.

Her answer is the thing to look at, because of what kind of answer it is.

She did not tell him he had imagined it, and she did not tell him to calm down. She told him that Allah would never disgrace him — and then she gave her evidence, which was entirely about the previous forty years.

You keep the ties of kinship. You carry the one who cannot carry himself. You give to the person who has nothing. You look after your guest. You help people through what is hard.

That is an argument. She is reasoning from a body of evidence she has had first-hand access to for a long time — she employed him before she married him — to a conclusion about what could and could not be happening to him now. A man who has lived like that is not a man Allah abandons to something terrible.

Then she acted. She took him to her cousin Waraqah ibn Nawfal, an old man who had studied the earlier scriptures, so that somebody who might recognise what this was could hear it described.

There is no record of her hesitating, and no record of her asking for a sign. The first person to believe the message was the person best placed to judge the messenger.

The account is in Sahih al-Bukhari, at the very beginning of the collection.