How can we be certain that the religion of Islam is addressed to all humanity from the time of the Prophet's mission until the Day of Judgment, considering that most of the Quranic verses and Prophetic hadiths were addressed to the people among whom the Prophet was sent?

If you believe in the prophethood of Muhammad (peace be upon him), then the proof of the universality of his message is his own declaration, as Allah Almighty says: "Say, 'O mankind, indeed I am the Messenger of Allah to you all,'" and "And We have not sent you, [O Muhammad], except as a warner and a bringer of good tidings to all mankind." The Prophet (peace be upon him) also stated that his message is universal to all people, whereas prophets before him were sent specifically to their own communities. There is also a consensus among Muslims regarding the universality of his message. It is contradictory for a person to believe in his prophethood and then doubt the truth of his pronouncements. The Prophet (peace be upon him) addressed all people of various faiths, and Islam is the sum of what he was sent with, encompassing creed and law. This religion must be conveyed purely and clearly to all people.