覆水盆に返らず

Etymology
. Originally read as in kanbun kundoku.

This form literally means "spilt water does not return to the basin". The back-formation of this form in pseudo-kanbun would be 覆水不返盆.

Proverb

 * 1) Once a married couple divorce, they cannot reconcile.
 * 2) don't cry over spilt milk.