Volume 8 · Book 76 · Hadith 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."
— Sahih Bukhari, Volume 8, Book 76: To make the Heart Tender (Ar-Riqaq), Hadith #499