Bite your tongue
bite your tongue means stop yourself from saying something that might upset somebody or cause an argument, although you want to speak.
Examples:
I didn’t believe her explanation but I bit my tongue.
Soraya: "Oh, I don't think I'm going to get the job."
Arsi: "Bite your tongue! You don't know that for sure.
All I can do is to bite my tongue if I want to keep my job.
