Musannaf Ibn Abi Shayba 33:313

Waki’ narrated to us, from Fitr, from Abu Ishaq, from Abu al-Ahwas, who said: Abdullah said: The believer sees his sin as if it were a boulder that he fears will fall upon him. The hypocrite sees his sin as a fly that landed on his nose, so he waved it away and it flew off.