What are the consequences for someone who chooses Islam after being given the choice between Islam or fighting, and is it valid for him to remain under his (previous) rule? And how can one reconcile the verse "There is no compulsion in religion" with the Hadith: "I have been commanded to fight the people until they say: 'There is no god but Allah'"?

Calling people to Islam is done by clarifying the concept of Tawhid (monotheism) to them with wisdom and good admonition, reminding them of Allah's blessings and warning them of His punishment. Everyone who is invited to Islam must respond to it and apply its commands to submit to Allah; otherwise, they will abide eternally in Hellfire. If a king embraced Islam, the Prophet, peace and blessings be upon him, would allow him to retain his kingdom, as stated in his letter to the kings of Oman. However, if a king refused Islam and prevented the du'at (preachers), it becomes permissible to fight him to clear the way for the da'wah (call to Islam).

The verse "There is no compulsion in religion" does not mean that disbelievers should not be fought. Rather, it signifies the absence of compulsion in matters of the heart, as the religion has clear proofs and does not require coercion. As for fighting disbelievers to subject them to Allah's rule and open the path for the call to Tawhid, this is firmly established in the Quran and Sunnah, as in His Almighty's saying: "And fight them until there is no fitnah (polytheism and disbelief) and [until] the religion, all of it, is for Allah."

Scholars have differed on the meaning of the verse "There is no compulsion in religion" with several opinions. Some say it is abrogated by the verses of fighting, or that it is specific to the People of the Book who pay jizyah (tribute), or that it was revealed concerning the Ansar and their children who had become Jewish, or about a man whose two sons had become Christian. It was also said that it means no compulsion for one who embraces Islam under duress, or that it applies to captives from the People of the Book who are not forced into Islam if they are adults, unlike idolaters who are compelled to embrace it.