Sunan Ibn Majah, Volume 2, Book 6, Hadith 1433 (DarusSalam) ⓘ

It was narrated that ‘Ali said that the Messenger of Allah said: “The Muslim has six courtesies due from the Muslim: He should greet him with Salam when he meets him; he should accept his invitation if he invites him; he should answer [by Yarhamuk-Allah (may Allah have mercy on you)] to him if he sneezes (and says Al- Hamdulillah); he should visit him if he falls sick; he should follow his funeral if he dies; and he should love for him what he loves for himself.”

حَدَّثَنَا هَنَّادُ بْنُ السَّرِيِّ، حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ أَبِي إِسْحَاقَ، عَنِ الْحَارِثِ، عَنْ عَلِيٍّ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏ "‏ لِلْمُسْلِمِ عَلَى الْمُسْلِمِ سِتَّةٌ بِالْمَعْرُوفِ يُسَلِّمُ عَلَيْهِ إِذَا لَقِيَهُ وَيُجِيبُهُ إِذَا دَعَاهُ وَيُشَمِّتُهُ إِذَا عَطَسَ وَيَعُودُهُ إِذَا مَرِضَ وَيَتْبَعُ جِنَازَتَهُ إِذَا مَاتَ وَيُحِبُّ لَهُ مَا يُحِبُّ لِنَفْسِهِ ‏" ‏ ‏.‏