don't tell him/her
Si tu ne lui dis pas, je le ferai.
If you don't tell him, I will.
Tu ne lui dis pas que tu as aussi sa cape et sa selle ?
You're not going to tell him that you also have his cape and saddle?
— Princesse Mononoké (1997)
Ne lui dis pas que j'ai dit ça.
Don't tell him I said that.
Don't tell him the answer.
Don't tell him that.
Ne lui dis pas que je suis en voyage.
Don't tell him/her that I'm traveling.
— On ne vit qu'une seule fois (2011)
Don't tell him why.