‘Umar ibn al-Khattab, a companion of the Prophet Muhammad (Allah bless him and give him peace), said:

As we sat one day with the Messenger of Allah (Allah bless him and give him peace), a man in pure white clothing and jet black hair came to us, without a trace of traveling upon him, though none of us knew him.

He sat down before the Prophet (Allah bless him and give him peace) bracing his knees against his, resting his hands on his legs, and said: "Muhammad, tell me about Islam." The Messenger of Allah (Allah bless him and give him peace) said: "Islam is to testify that there is no god but Allah and that Muhammad is the Messenger of Allah, and to perform the prayer, give alms, fast in Ramadan, and perform the pilgrimage to the House if you can find a way."

He said: "You have spoken the truth," and we were surprised that he should ask and then confirm the answer. Then he said: "Tell me about true faith (iman)," and the Prophet (Allah bless him and give him peace) answered: "It is to believe in Allah, His angels, His inspired Books, His messengers, the Last Day, and in destiny, its good and evil."

"You have spoken the truth," he said, "Now tell me about the perfection of faith (ihsan)," and the Prophet (Allah bless him and give him peace) answered: "It is to worship Allah as if you see Him, and if you see Him not, He nevertheless sees you."

(Sahih Muslim, 1.37: hadith 8)

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