They replied, “Messenger of Allah, he is suffering from his eyes,” that is, he has pain in them. The Prophet therefore sent for him; he came, and the Prophet spat into his eyes, whereupon they were healed instantly, as though he had never felt any pain at all—Allah is capable of all things. He then handed him the banner and said, “Advance, and do not look back until Allah grants victory.”
So ʿAlī—may Allah be pleased with him—went on. After a short distance he halted, yet he did not turn around, for the Prophet ﷺ had said, “Do not look back.” Raising his voice as loudly as he could, he called out, “Messenger of Allah, what shall I fight them for?”—still without turning his head, because the Messenger ﷺ had told him not to turn. The Prophet answered, “Fight them until they testify that lā ilāha illā Allāh and that Muhammad is the Messenger of Allah.”
This utterance is momentous; were the heavens and the earth weighed against it, it would outweigh them. By means of this word a person moves from disbelief to Islam; it is the very gateway to Islam: the testimony that there is no deity worthy of worship but Allah and that Muhammad is the Messenger of Allah. “When they do that, they have protected from you their blood and their wealth, except for its due, and their reckoning is with Allah.” That is, once they say, “We bear witness that there is no deity worthy of worship but Allah and that Muhammad is the Messenger of Allah,” they are not to be fought. Their lives and property are safeguarded, except for its due—that is, the rights that follow from lā ilāha illā Allāh. For lā ilāha illā Allāh is not a mere phrase uttered with the tongue; it has conditions and requirements that must be fulfilled.
Thus, when some of the early scholars were asked, “Did the Prophet ﷺ say that the key to Paradise is lā ilāha illā Allāh?” they replied, “Yes, the key to Paradise is lā ilāha illā Allāh, but work is still necessary, for a key needs ridges.” And the saying is true: a key needs ridges; if you bring a key with no ridges, it will not open for you.
Therefore, the Prophet’s words ﷺ, “except for its due,” embrace everything.