Sahih Bukhari
To make the Heart Tender (Ar-Riqaq)
Volume: 008 / Book Number: 076 / Hadith Number: 499
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 as destructive sins."