then say, “And upon you,” meaning: do not add “and peace be upon you,” for the Prophet himself explained the reason within the same ḥadīth. He said that when the Jews greet you they say al-sām ʿalaykum—invoking death upon you. Therefore the Messenger of Allah (peace and blessings be upon him) instructed: “Say, ‘And upon you,’” that is, “and upon you likewise be al-sām.” From this it is understood that if they were genuinely to say “Peace be upon you,” we would respond, “And upon you be peace,” and there is no harm in that, because Allah says: “When you are greeted with a greeting, respond with one that is better than it, or return it in like measure” (Q 4:86). Allah alone grants success.

845 – ʿAbdullāh ibn ʿAmr ibn al-ʿĀṣ relates that a man asked the Messenger of Allah (peace and blessings be upon him), “Which aspect of Islam is best?” He replied, “That you provide food, and that you offer the greeting of peace to those you know and to those you do not know.” Agreed upon.