Musnad Ahmad 236:1

Isma'il ibn Ibrahim narrated to us, he said: Sa'id al-Jurayri narrated to us, from Abu al-Sulayl, from Abu Tamimah al-Hujaymi—Isma'il said once: from Abu Tamimah al-Hujaymi, from a man of his people—he said: I met the Messenger of Allah (peace and blessings of Allah be upon him) on one of the roads of Medina, and he was wearing a cotton waist-wrapper (izar) with a frayed hem. I said: "‘Alayka al-salam (Upon you be peace), O Messenger of Allah." He said: "Indeed, ‘Alayka al-salam is the greeting of the dead. Indeed, ‘Alayka al-salam is the greeting of the dead. Indeed, ‘Alayka al-salam is the greeting of the dead. Salam ‘alaykum (Peace be upon you), Salam ‘alaykum," two or three times like that. He said: I asked about the waist-wrapper, and I said: "Where should I tie my waist-wrapper?" He raised his garment to the bone of his shin and said: "Here you should tie your waist-wrapper. If you refuse, then here, lower than that. If you refuse, then here, above the ankles. If you refuse, then indeed Allah, the Almighty and Majestic, does not love every arrogant boaster." He said: I asked him about good deeds, and he said: "Do not belittle anything of good, even if it is to give a piece of rope, or to give a sandal strap, or to pour from your bucket into the vessel of one seeking water, or to remove something from the path of the people that harms them, or to meet your brother with a cheerful face, or to meet your brother and greet him, or to comfort the lonely in the land. And if a man insults you for something he knows about you, while you know the like of it in him, do not insult him, so that the reward is yours and the sin is upon him. And whatever pleases your ear to hear, act upon it, and whatever displeases your ear to hear, avoid it."