[Explanation]
This chapter is cited by the author in Riyāḍ al-Ṣāliḥīn under the ruling on giving the greeting of salām to outright disbelievers and to those living intermixed with Muslims. We have already discussed greeting committed Muslims and established that it is a strongly confirmed sunnah. As for greeting disbelievers, it is not permissible for us to initiate them with the salām. In other words, if a person passes by a non-Muslim or enters upon him, he may not say, “Peace be upon you,” because the Prophet ﷺ forbade it, as related in the ḥadīth of Abū Hurayrah (may Allah be pleased with him).

The reason is that extending salām to them contains a degree of submission and a kind of honouring, for greeting someone is itself an act of honour. The disbeliever is not entitled to such honour; rather, what he deserves from us is that we vex, humble, and abase him. Allah, exalted be He, says:

“Muhammad is the Messenger of Allah; and those who are with him are harsh against the disbelievers, merciful among themselves. You see them bowing and prostrating, seeking bounty from Allah and His pleasure. Their marks are on their faces from the trace of prostration. Such is their description in the Torah, and their description in the Gospel: like a plant that puts forth its shoot, then strengthens it, and it grows stout and stands firm upon its stalk, delighting the sowers—so that through them He may enrage the disbelievers…” ⦗48:29⦘

—this is the textual proof. And the Exalted also says in Sūrat al-Tawbah: “And do not…⦗…⦘”