Vague predictions of the future and lead one to adventure.
Saints and Sainthood: The inside story on the ascended
“Dreams are the only reality” suggests some of the ancient manuscripts. Dreams and the dreamers often reveal secrets long forgotten, or dreams can hide the truth only to make it resurface decades or even centuries later
A rumour of the knights of some powerful king that sleep until danger threatens the kingdom.
The truth is that they were rebels, trying to split the kingdom. Once captured they were put into an enchanted sleep, protected from age and harm, until their aims have been carried out by others in which case they will awaken.
There is a loophole in the spell in that trying to take one of their weapons will also awaken them.