John Cassian, The Institutes IX.5: That disturbances are caused in us not by the faults of other people, but by our own

Whence it is clearly proved that the pains of disturbances are not always caused in us by other people’s faults, but rather by our own, as we have stored up in ourselves the causes of offence, and the seeds of faults, which, as soon as a shower of temptation waters our soul, at once burst forth into shoots and fruits.