Looking for a quote from a certain episode

[hxclespaulplayer]

It's when O'brien mentions that he would feel bad even killing a fly/bug. I assumed that it was in relation to having to kill someone, and obviously thought "Hard Time" would have been the episode, but it's not in the script.

 

[Andymator]

It's from TNG's "The Wounded".

 

[CorporalCaptain]

Yep, it appears so. From http://www.chakoteya.net/NextGen/186.htm:

O'BRIEN: The only people left alive were in an outlying district of the settlement. I was sent there with a squad to reinforce them. Cardassians were advancing on us, moving through the streets, destroying, killing. I was with a group of women and children when two Cardassian soldiers burst in. I stunned one of them. The other jumped me. We struggled. One of the women threw me a phaser, and I fired. The phaser was set at maximum. The man just incinerated, there before my eyes. I'd never killed anything before. When I was a kid, I'd worry about swatting a mosquito. It's not you I hate, Cardassian. I hate what I became because of you.