The reply letter from Tito following an assassination attempt from Stalin is one of the great political correspondences of the era: https://en.wikipedia.org/wiki/Tito%E2%80%93Stalin_split?wpro...
Is the quote in this section?
https://en.wikipedia.org/wiki/Josip_Broz_Tito#Tito%E2%80%93S...
"Stop sending people to kill me. We've already captured five of them, one of them with a bomb and another with a rifle. [...] If you don't stop sending killers, I'll send one to Moscow, and I won't have to send a second."