SuttaCentral
I’ve heard of a story where a blind monk who is an arahant is stepping on insects while walking and thereby kills them. He is criticized by other monks, but the Buddha comes to his defense, saying he is not acting with any bad intention.
As far as I can see this is not a story from the Suttas. Does anyone know where it is told?
It is from the Dhammapada stories, the background story of the first verse of the Dhammapada.
“Reverend Sir, the Elder Cakkhupāla, saying to himself, ‘I will take a walk,’ has destroyed many insects.” “But did you see him killing them?” “We did not, Reverend Sir.” “Precisely as you did not see him, so also did he not see these insects. Monks, they that are freed from the Depravities have no thought of killing.”
https://www.ancient-buddhist-texts.net/English-Texts/Buddhist-Legends/01-01.htm
I am very impressed! Thank you so much!! 
The pali can be found here, but apparently something is broken in Tipitaka.org as I when I click the link to yamakavaggo I get an HTTP 400 error…
Not the PDFs are working:
Tipiṭaka in PDF (tipitaka.org)
Venerable @sabbamitta, I found this another resource which seems to contain the pali original for Cakkhupala’s story:
Pāli: KN-a 2 - 1. cakkhupālattheravatthu (digitalpalireader.online)
The most referenced part of the story is found from the paragraph starting with:
" atha kho te gantvā tathāgatassa ārocesuṃ, “bhante, cakkhupālatthero ‘caṅkamāmī’ti bahū pāṇake māresī”ti. “kiṃ pana so tumhehi mārento diṭṭho”ti? “na diṭṭho, bhante”ti… (…)"
Which roughly translates as :
Then those people went to the Tathāgata and informed him, “Bhante, they say that the elder Cakkhupāla kills many living beings.” The Buddha asked, “But was it seen by you that he killed them?” They replied, “No, Bhante.” (…)
It is also found here:
tipitaka.org/romn/cscd/s0502a.att1.xml
There is no intention to harm these insects and I am sure if he had the capacity to avoid them in that moment the Monk would have.
The motive and intention defines/charges the action.