leave undone

That which thou wouldst not, thou must oftentimes do; and that which thou wouldst, thou must leave undone.

Lamotte contented himself with looking on the event, ready to finish with his spear what Lachane might leave undone.

The functions of the Anglo-Irish Government were to do what ought not to be done, and to leave undone what ought to be done.

You're like the feller in Scriptur', you leave undone the things you ought to do and do them that—All right, Jim!

There are things that a plain esquire may leave undone without causing scandalised remark, but a fiercer light beats on a baron.