(449) بَابُ مَنْ بَدَأَ بِالسَّلامِ
Abu Ayyub reported that the Messenger of Allah, may Allah blesshim and grant him peace, said, "It is not lawful for a Muslim man to separatehimself from his brother for more than three days. When they meet, andone turns away and the other turns away, the better of them is the onewho gives the greeting first."
Reference: Al-Adab Al-Mufrad 985
In-book reference: Book 42, Hadith 21
English translation: Book 42, Hadith 985