A man passed by the Messenger of Allah ﷺ while he was sitting in a gathering and said, "Peace be upon you."The Prophet ﷺ said, "Ten good deeds."Then another man passed by and said, "Peace be upon you and the mercy of Allah."He said, "Twenty good deeds."Then another man passed by and said, "Peace be upon you and the mercy of Allah and His blessings."He said, "Thirty good deeds."Then a man got up from the gathering and left without giving the greeting of peace. The Prophet ﷺ said, "How quickly your companion forgot! When one of you comes to a gathering, let him give the greeting of peace. If he wishes to sit, let him sit. And when he gets up to leave, let him give the greeting of peace, for the first is no more deserving than the last."
أن رجلا مر على رسول الله ﷺ، وهو في مجلس، فقال: سلام عليكم. فقال: عشر حسنات. ثم مر رجل آخر فقال: سلام عليكم ورحمة الله. فقال: عشرون حسنة، فمر رجل آخر فقال: سلام عليكم ورحمة الله وبركاته. فقال: ثلاثون حسنة. فقام رجل من المجلس ولم يسلم، فقال النبي ﷺ: ما أوشك ما نسي صاحبكم! إذا جاء أحدكم إلى المجلس فليسلم، فإن بدا له أن يجلس فليجلس، فإن قام فليسلم، فليست الأولى بأحق من الآخرة.
Bukhari narrated it in Adab al-Mufrad (986) from Abdul-Aziz bin Abdullah, who said, "Muhammad bin Jafar bin Abu Kathir narrated to me, from Yaqub bin Zayd Taymi, from Saeed Maqburi, from Abu Hurairah," and he mentioned it. Ibn Hibban graded it sahih (493), and he transmitted it from Umar bin Muhammad Hamdani, who said, "Muhammad bin Ismail Bukhari narrated to us," and he mentioned it. Its isnad is sahih.