Language:
كتاب الرقاق
81
To make the Heart Tender (Ar-Riqaq)
(32)
Chapter: What minor sins should be warded off
(32)
باب مَا يُتَّقَى مِنْ مُحَقَّرَاتِ الذُّنُوبِ

Narrated Ghailan:

Anas said "You people do (bad) deeds (commit sins) which seem in your eyes as tiny (minute) than hair while we used to consider those (very deeds) during the life-time of the Prophet (ﷺ) as destructive sins."

حَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا مَهْدِيٌّ، عَنْ غَيْلاَنَ، عَنْ أَنَسٍ ـ رضى الله عنه ـ قَالَ إِنَّكُمْ لَتَعْمَلُونَ أَعْمَالاً هِيَ أَدَقُّ فِي أَعْيُنِكُمْ مِنَ الشَّعَرِ، إِنْ كُنَّا نَعُدُّهَا عَلَى عَهْدِ النَّبِيِّ صلى الله عليه وسلم الْمُوبِقَاتِ‏.‏ قَالَ أَبُو عَبْدِ اللَّهِ يَعْنِي بِذَلِكَ الْمُهْلِكَاتِ‏.‏
Reference : Sahih al-Bukhari 6492
In-book reference : Book 81, Hadith 81
USC-MSA web (English) reference : Vol. 8, Book 76, Hadith 499
  (deprecated numbering scheme)