Anas b. Mālik – Allah be pleased with him – said:

You people do things today that you regard as less significant than a strand of hair, whereas we, during the time of the Prophet – peace and blessings be upon him – used to consider them destructive sins.

Al-Bukhārī in his Ṣaḥīḥ, Chapter on sins that are seen as insignificant but which should be kept away from.