Help - quote!

Hello, lads!

I am writing paper for my university (civil engineering) and I want to quote Tolstoy, but I am not sure from where is it: Anna Karenina or War and Peace (probably W&P), others are excluded surely.
Quote goes something like: When two are in fight/quarrel, they are always both wrong.

I've tried boolean search, but nothing comes up.
I can write that it's from W&P, but it just wouldn't be fair :D

Thanks!

Don't recall that line from Anna Karenina, am currently reading W&P and have not come across anything like that line yet.