كتاب الإيمان
1
The Book of Faith
(19)
Chapter: Encouragement to honor one's neighbor and guest, and the obligation to remain silent unless one has something good to say, and the fact that all of that is part of faith
(19)
باب الْحَثِّ عَلَى إِكْرَامِ الْجَارِ وَالضَّيْفِ وَلُزُومِ الصَّمْتِ إِلاَّ مِنَ الْخَيْرِ وَكَوْنِ ذَلِكَ كُلِّهِ مِنَ الإِيمَانِ

It is narrated on the authority of Abu Shuraih al-Khuzai' that the Prophet (may peace and blessings of Allah be upon him) observed:

He who believes in Allah and the Last Day should do good to his neighbour and he who believes in Allah and the Last Day should show hospitality to the guest and he who believes in Allah and the Last Day should either speak good or better remain silent.
حَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ، وَمُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، جَمِيعًا عَنِ ابْنِ عُيَيْنَةَ، - قَالَ ابْنُ نُمَيْرٍ حَدَّثَنَا سُفْيَانُ، - عَنْ عَمْرٍو، أَنَّهُ سَمِعَ نَافِعَ بْنَ جُبَيْرٍ، يُخْبِرُ عَنْ أَبِي شُرَيْحٍ الْخُزَاعِيِّ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ ‏ "‏ مَنْ كَانَ يُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ فَلْيُحْسِنْ إِلَى جَارِهِ وَمَنْ كَانَ يُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ فَلْيُكْرِمْ ضَيْفَهُ وَمَنْ كَانَ يُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ فَلْيَقُلْ خَيْرًا أَوْ لِيَسْكُتْ ‏"‏ ‏.‏
Reference : Sahih Muslim 48
In-book reference : Book 1, Hadith 83
USC-MSA web (English) reference : Book 1, Hadith 78
  (deprecated numbering scheme)