Is the husband's oath that the Prophet, may God's prayers and peace be upon him, knows what is in the Preserved Tablet and the Pen considered disbelief that expels him from Islam, and thus invalidates the marriage contract?

None knows the unseen save Allah the Almighty, and no one, not even prophets and messengers, can know what is in the Preserved Tablet (Al-Lawh Al-Mahfuz) except by Allah's permission and His informing them of some of it. Allah did not inform His Prophet Muhammad, peace be upon him, of everything in the Preserved Tablet; had He done so, the Prophet would have known all of the unseen, including the time of the Hour. It is established in the Quran and Sunnah that the Prophet, peace be upon him, did not know the entire unseen, and he was forbidden from claiming that.

The claim that the Prophet, peace be upon him, knows the entire unseen, including what is in the Preserved Tablet, is a false belief and considered disbelief by some scholars, because it involves exaggeration regarding him, peace be upon him, and attributing complete knowledge of the unseen to other than Allah.

If the husband believes that the Prophet, peace be upon him, knows what is in the Preserved Tablet, then his statement is disbelief, but he is not judged to be a disbeliever until proof is established against him and the truth is clarified to him. The wife should advise her husband gently and explain the evidence from the Quran and Sunnah that affirms that knowledge of the unseen is exclusive to Allah alone.