Sahih Bukhari Volume 8, Book 81, Hadith 6494

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.‏

Narrated By 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 as destructive sins."