I believe there is a Dhammapada story (non-canonical) where an arahant steps on some bugs and kills them. Some other monks blame him but the Buddha maintains that since this monk was an arahant, there was no evil intention behind this act.
The story is explaining the most famous verse of the Dhammapada ~ Verse 1. But the main point is that he was blind - there was no intention.
Chapter 1 - Yamaka 1 Vagga The Twin Verses (Text and Translation by Ven. Narada)1. Manopubbangama dhamma 2
Manasa ce padutthena
bhasati va karoti va
Tato nam dukkhamanveti
cakkam'va vahato padam. 1
.EVIL BEGETS EVIL
1. Mind is the forerunner of (all evil) states. 3 Mind is chief; mind-made are they.
If one speaks or acts with wicked mind, because of that, suffering follows one, even as the wheel follows the hoof of the draught-ox. 1.Story
A middle-aged devout person, named Cakkhupala, became a monk and was energetically leading a contemplative life. As a result of his strenuous endeavour he realized Arahantship, 4 the final stage of Sainthood, but unfortunately went blind.
One day as he was pacing up and down the ambulatory he unintentionally killed many insects. Some visiting monks, noticing the blood-stained ambulatory, complained to the Buddha that he had committed the offence of killing. The Buddha explained that the monk had killed them unintentionally and that he was an Arahant.
The monks then wished to know the cause of his blindness.
The Buddha related that in a past birth, as a physician, that particular monk had given an ointment to a poor woman to restore her eyesight. She promised that, with her children, she would become his servants if her eyesight was restored. The physician's remedy proved effective, but the woman, not willing to keep her promise, pretended that her eyes were getting worse. The cruel physician, yielding to a wicked thought, retaliated by giving her another ointment which blinded her eyes. In consequence of his past evil action the Arahant became blind.
* * *
This is the retributive aspect of the law of Kamma, the other being the continuative aspect, that is - the transmission of individual characteristics, impressions, tendencies, etc. throughout one's wanderings in Samsara.
An Arahant, though free from all impurities, has to reap the fruit of the seed he himself had sown in the remote past.
The Buddhas and Arahants do not accumulate fresh Kamma as they have eradicated the roots - ignorance and craving- but, as every other being, they are not exempt from the inevitable consequences of both good and bad past actions.http://home.nethere.net/dsparks/narada/ ... 0Vagga.htm