What is the ruling on the Bay'ah (oath of allegiance)? Is it permissible for a Muslim to pledge allegiance to a group? And is it permissible to engage in secret da'wah (Islamic proselytizing) work for the service of the religion?

Proclaiming the دعوت (call/message) publicly is the fundamental principle for achieving the transmission of religion, clarifying the truth, and resisting falsehood. Secrecy, on the other hand, is an exception dictated by the interest of the دعوت, its protection, and ensuring its continuity. The دعوت was initially secret until it gained strength, whereupon Allah commanded His Prophet to proclaim it publicly. Secrecy or public proclamation is not a fixed stage but rather a need and an interest determined by the circumstances of reality. The principle of secrecy or public proclamation should not be a cause of dispute among the people of the دعوت, especially since the falsehoods are plotting and scheming against Islam and its people.