goes without saying; needless to say
Used to state that something is so obvious it doesn't need to be mentioned. Often appears as a sentence-initial or parenthetical phrase.
It goes without saying that health is the most important thing.
Needless to say, being late is strictly forbidden.
expression, noun which may take the genitive case particle 'no'
better left unsaid; shouldn't be said
Used to indicate that something is better not mentioned, often because it is tactless, unnecessary, or might cause trouble. Can modify a noun with の.
It's better not to mention his mistake.
That was a piece of advice better left unsaid.