Al-Kāfi - Volume 2 > The One Who Must Offer the Greeting of Peace
Hadith #5

5ـ مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ عُمَرَ بْنِ عَبْدِ الْعَزِيزِ عَنْ جَمِيلٍ عَنْ أَبِي عَبْدِ الله (عَلَيهِ السَّلام) قَالَ إِذَا كَانَ قَوْمٌ فِي مَجْلِسٍ ثُمَّ سَبَقَ قَوْمٌ فَدَخَلُوا فَعَلَى الدَّاخِلِ أَخِيراً إِذَا دَخَلَ أَنْ يُسَلِّمَ عَلَيْهِمْ.

5. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from ‘Umar ibn ‘Abd al-‘Aziz from Jamil from abu ‘Abd Allah (a.s.) who has said the following: “If two groups attend the same meeting, the group entering last should offer greetings of peace to those who have entered first.”