I define Islam for you in a way that nobody dared do it before me. Islam means obedience to God, obedience to God means having sincere faith in Him, such a faith means to believe in His Power, belief in His Power means recognizing and accepting His Majesty, acceptance of His Majesty means fulfilling the obligations laid down by Him and fulfillment of obligations means actions (Therefore, Islam does not mean mere faith, but faith plus deeds).

Ali bin Abu-Talib
Another Quote