(448) بَابُ إِفْشَاءِ السَّلامِ
Abu Hurayra reported that the Prophet, may Allah bless him andgrant him peace, said, "You will not enter the Garden until you believeand you will not believe until you love one another. Shall I tell you somethingthe doing of which will give you love of one another?" "Yes, Messengerof Allah," they replied. The Prophet said, "Make the greeting common practiceamong you."
Reference: Al-Adab Al-Mufrad 980
In-book reference: Book 42, Hadith 16
English translation: Book 42, Hadith 980