About fifteen minutes into 6x23 Rightful Heir, Kahless reminds Worf of a vision Worf had when he was young. But later on it is revealed that
Kahless is actually a clone with imprinted memories from the scriptures, which certainly don't include a vision had by a back then pretty unknown young Klingon.
So how does he know? Or, since Worf doesn't seem to remember, did Kahless make it up? But that would not be honorable, something a Kahless certainly wouldn't consider.