Reference: Musnad al-Imaam Ahmad – Volume 5, Page 331
Sahl ibn Sa’d (radhi-yAllaahu ‘anhu) narrated that Allaah’s Messenger ﷺ said:
Beware of sins which are treated as being minor, just like a people who encamp in the centre of a valley, so someone brings a stick of firewood and someone else brings a stick until they are therefore able to bake their bread. Likewise sins which are treated as being minor and for which the person is taken to account will destroy him.