Sayyiduna Husayn bin Ali (may Allah be pleased with him) narrates from Sayyiduna Ali (may Allah be pleased with him) that he said that the Messenger of Allah (peace and blessings be upon him) said: "After faith, the very essence of wisdom (and its greatest part) is to treat people with love and friendliness."
Hadith Referenceالمعجم الأوسط / باب العين / 4847
Hadith Takhrij«أخرجه الطبراني فى «الصغير» برقم: 705»