Praise be to Allah.
Everything that the Messenger (peace and blessings of Allaah be upon him) has told us about the unseen, past, present and future, such as the beginning of creation, the resurrection, Paradise, Hell, the signs of the Hour, the angels and the Prophets, all of that is by revelation (wahy) from Allaah, as Allaah says (interpretation of the meaning):
“Nor does he speak of (his own) desire. It is only a Revelation revealed” (al-Najm 53:3-4)
“This is of the news of the Unseen which We reveal unto you (O Muhammad)” [Hood 11:49]
“Say (O Muhammad): ‘I don’t tell you that with me are the treasures of Allaah, nor (that) I know the Unseen; nor I tell you that I am an angel. I but follow what is revealed to me.’” [al-An’aam 6:50]
Hence it is obligatory to believe everything that Allaah has told the Messenger (peace and blessings of Allaah be upon him) concerning the unseen and other matters, for he is the one who tells the truth and is to be believed. Whoever disbelieves him, even if it is with regard to only one report that he knows to be sound (saheeh), becomes an apostate thereby, if he is Muslim.