Mishkat al-Masabih 1524
Abu Huraira reported God’s messenger as saying, “A Muslim has five duties towards another Muslim:
to return a salutation, visit the sick, follow funerals, accept an invitation and say ‘God have mercy on you’ when one sneezes.”

(Bukhari and Muslim.)
وَعَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: 
" حَقُّ الْمُسْلِمِ عَلَى الْمُسْلِمِ خَمْسٌ: رَدُّ السَّلَامِ وَعِيَادَةُ الْمَرِيضِ وَاتِّبَاعُ الْجَنَائِزِ وَإِجَابَةُ الدعْوَة وتشميت الْعَاطِس "