Abu Hurayra reported that a man passed by the Messenger of Allah, may Allah bless him and grant him peace, while hew as in an assembly and said, "Peace be upon you." "Ten good deeds," he said. Another man passed by and said, "Peace be upon you and the mercy of Allah." The Prophet said, "Twenty good deeds." Then yet another man passed by and said, "Peace be upon you and the mercy of Allah and His blessing," and the Prophet said, "Thirty good deeds." Then a man in the gathering got up and did not give the greeting. The Messenger of Allah, may Allah bless him and grant him peace, said, "How quickly your companion forgets! When one of you comes to an assembly, he should give the greeting. If he thinks he should sit down, he sits down. When he stands up, he gives the greeting. Neither is a greater duty than the other."  

أَنَّ رَجُلاً مَرَّ عَلَى رَسُولِ اللهِ ﷺ وَهُوَ فِي مَجْلِسٍ فَقَالَ السَّلاَمُ عَلَيْكُمْ فَقَالَ عَشْرُ حَسَنَاتٍ فَمَرَّ رَجُلٌ آخَرُ فَقَالَ السَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللهِ فَقَالَ عِشْرُونَ حَسَنَةً فَمَرَّ رَجُلٌ آخَرُ فَقَالَ السَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللهِ وَبَرَكَاتُهُ فَقَالَ ثَلاَثُونَ حَسَنَةً فَقَامَ رَجُلٌ مِنَ الْمَجْلِسِ وَلَمْ يُسَلِّمْ فَقَالَ رَسُولُ اللهِ ﷺ مَا أَوْشَكَ مَا نَسِيَ صَاحِبُكُمْ إِذَا جَاءَ أَحَدُكُمُ الْمَجْلِسَ فَلْيُسَلِّمْ فَإِنْ بَدَا لَهُ أَنْ يَجْلِسَ فَلْيَجْلِسْ وَإِذَا قَامَ فَلْيُسَلِّمْ مَا الأُولَى بِأَحَقَّ مِنَ الآخِرَةِ