Musnad Ahmad 26:477

Abu Kamil and Yazid narrated to us, al-Mas'udi informed us, from al-Hasan ibn Sa'd, from 'Abdah al-Nahdi, from Abdullah ibn Mas'ud, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah has not prohibited a prohibition except that He knew that someone among you would eventually violate it. Behold, I am holding onto your waistbands so that you do not fall into the Fire like the falling of moths and flies." Yazid said: "Moths or flies."