Is what the questioner said—of his intention to strike another person after Satan whispered to him that he meant the Prophet Muhammad (peace be upon him)—considered disbelief, and what are the implications of that regarding his marriage contract?

These obsessive thoughts do not take one out of the fold of Islam, as long as the person does not intentionally commit acts or utter statements of disbelief. Nor do they affect marital 'ismah (protection/infallibility). Therefore, one should divert their mind from these thoughts and occupy their time with productive work or permissible recreation.