Because the old expression about the child being the father of the man is quite true.

You've heard that old expression, to follow one to the ends of the earth.

"It is an old expression, and you are very much a policeman."

What's the old expression about not seeing the forest for the trees?

As the old expression goes, it seemed like a good idea at the time.

There's an old expression that you shouldn't mix business with pleasure.

It is an old expression which goes back to the days when writers were paid one penny for each line they wrote.

Now she understood what was meant by the old expression about seeing stars.

The music, does it pass out of one ear and into another, as the old expression goes?

There is an old expression in English which says that charity begins at home.