hold one's tongue

The vast moral importance of being able to hold one's tongue, the golden resources of silence, should be emphasized by the teacher.

And then, seeing these things, people want a—well, better hold one's tongue!

That night I spake to Sonnlein kindly but firmly, reminding him how poorly it accorded with his manhood's estate to indulge in such levity; that even if he could not always agree with the hair-splitting speculations of our worthy superintendent, it were surely wiser to hold one's tongue lest that unruly member poison all our peace.

Oh, there's plenty of mystery about it all; and, once more, it's better to hold one's tongue!

At least this once, one could hold one's tongue.