What are the Prophetic narrations (Hadith) indicating the obligation of believing in the Unseen?

Belief in the unseen encompasses all pillars of faith. Al-Bukhari reported from Abu Hurayrah, may Allah be pleased with him, that the Prophet, peace and blessings be upon him, said: "Faith is to believe in Allah, His angels, in meeting Him, His messengers, and to believe in resurrection." Ahmad also reported from Ibn Abbas, may Allah be pleased with them both, in the long Hadith of Gabriel, that faith is: "To believe in Allah, the Last Day, His angels, the Book, the Prophets, to believe in death and life after death, to believe in Paradise, Hellfire, the reckoning, and the balance, and to believe in divine decree, all of it, its good and its evil." Al-Tirmidhi reported from Ali, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, said: "A servant does not believe until he believes in four things: he bears witness that there is no god but Allah and that I am Muhammad, the Messenger of Allah, whom He sent with the truth; he believes in death and in resurrection after death; and he believes in divine decree." Al-Hakim and Al-Dhahabi authenticated that Abdullah ibn Mas'ud said: "By Him besides whom there is no god, no believer has believed better than one who believes in the unseen," then he recited the verse: "Alif, Lam, Meem. This is the Book about which there is no doubt, a guidance for those conscious of Allah. Who believe in the unseen."