How can one reconcile God alone knowing the unseen, with some people seeing things in dreams that later come true, or their seeing Paradise and Hell in their sleep?

The true unseen (Al-Ghaib Al-Haqiqi) is known only to Allah the Almighty. However, He reveals parts of it to some of His servants through four ways:

1. Through the angel to the prophets: Informing them of future signs of the Hour and news of Paradise and Hell. 2. Through truthful dreams (Ar-Ru'ya As-Sadiqa): Where a person sees what will happen to them or to others in the future. This can be a part of prophethood. 3. Through divine inspiration (At-Tahdith wal-Ilham): As happened to Umar ibn Al-Khattab and the mother of Musa. This can occur in a waking state or in a dream, and through a voice. 4. Through direct speech from Allah to His messenger: As occurred to our Prophet, peace and blessings be upon him, on the night of Al-Mi'raj (the Ascension).

Truthful dreams will become more frequent towards the End of Times, and they are among the good tidings. A Muslim's dream is one part of forty-six parts of prophethood.