كتاب الإيمان
1  
The Book of Faith
(34)
Chapter: Clarifying that faith decreases with shortcoming in obedience, and the word Kufr may be used with regard to matters other than dsbelief in Allah, such as ingratitude for blessings and not fulfilling one's duties
(34)
باب بَيَانِ نُقْصَانِ الإِيمَانِ بِنَقْصِ الطَّاعَاتِ وَبَيَانِ إِطْلاَقِ لَفْظِ الْكُفْرِ عَلَى غَيْرِ الْكُفْرِ بِاللَّهِ كَكُفْرِ النِّعْمَةِ وَالْحُقُوقِ
Sahih Muslim 79 b
This hadith has been narrated on the authority of Abu Tahir with this chain of transmitters.
وَحَدَّثَنِيهِ أَبُو الطَّاهِرِ، أَخْبَرَنَا ابْنُ وَهْبٍ، عَنْ بَكْرِ بْنِ مُضَرَ، عَنِ ابْنِ الْهَادِ، بِهَذَا الإِسْنَادِ مِثْلَهُ ‏.‏
Reference : Sahih Muslim 79b
In-book reference : Book 1, Hadith 148
USC-MSA web (English) reference : Book 1, Hadith 142
  (deprecated numbering scheme)