Muʿādh, by Allah, I truly love you. Then I counsel you, O Muʿādh: never omit, at the close of every prayer, to say: “O Allah, help me to remember You, to thank You, and to worship You with excellence.” Reported by Abū Dāwūd and al-Nasāʾī with an authentic chain.

11/385 — Anas (may Allah be pleased with him) narrated: A man was sitting with the Prophet ﷺ when another man passed by. The first said, “Messenger of Allah, I love that man.” The Prophet ﷺ asked, “Have you informed him of it?” He replied, “No.” The Prophet ﷺ said, “Inform him.” He caught up with the man and said, “I love you for the sake of Allah.” The other answered, “May the One for whose sake you love me also love you.” Reported by Abū Dāwūd with a sound chain.

[Explanation]
All these narrations deal with love, teaching that a person’s love should be for Allah and in Allah. In the hadith cited earlier by the author (may Allah have mercy on him), the Prophet ﷺ said: “By Him in whose hand is my soul, you will not enter Paradise until you believe, and you will not truly believe until you love one another. Shall I direct you to something which, if you do it, you will come to love one another? Spread the greeting of peace among yourselves.”

This shows that love is part of the perfection of faith, that a servant’s faith is incomplete until he loves his brother, and that one of the causes of mutual love is to spread the greeting of peace among one’s fellow believers—that is, to make it manifest and widespread, greeting every believer one meets, whether one knows him or not. This fosters love; when someone passes by and greets you with salām, you feel affection toward him, whereas if he withholds the greeting you instinctively dislike him, even if he were the closest of people to you.