Abu Hurayra reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "When one of you comes to a gathering, he should give the greeting. If he leaves, he should give the greeting. Neither is more of a duty than the other."  

قَالَ رَسُولُ اللهِ ﷺ إِذَا جَاءَ أَحَدُكُمُ الْمَجْلِسَ فَلْيُسَلِّمْ فَإِنْ رَجَعَ فَلْيُسَلِّمْ فَإِنَّ الأُخْرَى لَيْسَتْ بِأَحَقَّ مِنَ الأولَى