What are the consequences of an Oath of Disbelief?

Assalaam Alaikum Mufti Sahab,

I am from India.
Please provide references from the Quran Sharif and Hadith. What are the Consequences of an Oath of Disbelief? If a person takes an oath saying “if I do this or do not do this, I will become a kafir forever”. If he or she breaks the oath will he or she become a kafir?

Note: I get a lot of waswasas, that a person becomes a kafir if he or she makes these types of oaths. Please help. JazakAllah

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