(28) باب مَا جَاءَ فِي كَرَاهِيَةِ أَنْ يَقُولَ عَلَيْكَ السَّلاَمُ مُبْتَدِئًا
Narrated Abu Tamimah Al-Hujaimi:
from a man among his people, who said: "I went looking for the Prophet (ﷺ) but I was not able to find him. So I sat down, and then I saw a group of people, and he was among them, but I did not recognize him. He was settling some matter between them so when he was finished, some of them stood up with him and they were saying: 'O Messenger of Allah.' When I saw that, I said: "'Alaikas-Salam (upon you be peace) O Messenger of Allah! 'Alaikas-Salam (upon you be peace) O Messenger of Allah! 'Alaikas-Salam (upon you be peace) O Messenger of Allah!' He replied: 'Indeed "'Alaikas-Salam (upon you be peace)" is the greeting for the dead.' Then he came toward me and said: 'When a man meets his Muslim brother then he should say: "As-Salamu 'Alaikum Wa Rahmatullahi Wa Barakatuh (peace be upon you, and the mercy and blessings of Allah)." Then the Prophet (ﷺ) responded to my greeting, he said: 'And may Allah's mercy be upon you, and may Allah's mercy be upon you, and may Allah's mercy be upon you.'"
Reference: Jami` at-Tirmidhi 2721
In-book reference: Book 42, Hadith 34
English translation: Vol. 5, Book 40, Hadith 2721