He ought to reply, “I have understood,” not, “You have spoken the truth.” Gabriel—peace be upon him—already knew the answer, and that is why he said, “You have spoken the truth.”

As for his request, “Inform me about faith,” faith (īmān) resides in the heart, whereas Islam manifests on the limbs; therefore we say: Islam is outward practice, while faith is an inward reality anchored in the heart.

Faith, then, is a person’s firm conviction—so certain that it admits neither doubt nor the slightest misgiving. One believes in it as surely as one believes in the midday sun, without the least hesitation: an unshakeable affirmation that wholeheartedly accepts what has come in Allah’s law and submits to it in full.

Thus he said: “Faith is that you believe in Allah—‘The month of Ramaḍān is the month in which the Qur’an was sent down’ (al-Baqarah 2:185)—and in His angels, His books, His messengers, the Last Day, and that you believe in the pre-decree, its good and its evil.” These are the six pillars, the pillars of faith.

His words, “that you believe in Allah,” mean that you affirm that Allah, exalted is He, exists; that He is living, all-knowing, all-powerful; that He alone is the Lord of all worlds, with no lord besides Him; that absolute sovereignty belongs to Him, all praise is His, and to Him all matters return. He alone deserves worship; none other is entitled to any share of it. On Him alone is reliance placed; from Him come victory and success. He possesses every attribute of perfection in a manner that does not resemble the attributes of created beings, for He says, “There is nothing like unto Him” (ash-Shūrā 42:11). In short, you believe in Allah’s existence, His lordship, His exclusive right to be worshipped, and in His names and attributes.