Change the narration: "Be polite to others" I said to him."
Explanation
Direct Speech: "Be polite to others," I said to him.
This is an imperative sentence (a command or advice).
In indirect speech:
Imperative sentences change into infinitive form (to + verb).
"Said to" becomes advised (since it's about good behavior).
So, the correct transformation is:
I advised him to be polite to others.
