Ibn ‘Umar (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "The worst lie is when a man claims to have seen something which he has not seen.”
The Prophet (may Allah's peace and blessings be upon him) explained that one of the worst types of lies is for a person to claim to have seen something, while awake or in his dreams, and he has not actually seen it. Lying about seeing something in a dream is worse than lying about seeing something in wakefulness, because what a person sees while being asleep is from Allah, the Almighty, via the angel if it is a vision. Therefore, lying in this case is considered lying about Allah. As for dreams, they are from the devil, and self-talk comes from the self. So, what the sleeping person sees is one of these three types.