Is it permissible to conceal polytheism (shirk billah) after repenting from it, even by lying? And what is the most appropriate action for a person suffering from pathological doubt when asked about something he doubts and that represents an accusation against him, such as someone who doubted that he committed adultery and was asked about it?

One who commits a sin, especially shirk (polytheism), must conceal it and hasten to repent by abandoning it, renewing their entry into Islam, and performing ghusl (ritual bath). If asked about it, they should remain silent or use tawriyah (ambiguity). As for one who suffers from obsessive whispers about committing sins, they must completely disregard them and seek refuge with Allah from Satan. Certainty is not dispelled by doubt, and the fundamental principle for a Muslim is soundness and blamelessness.