Full Idea
Actions are morally good in virtue of their motives; this is quite distinct from rightness, which belongs to act in virtue of the nature of what is done. So a good action may not do what is right, and a right action need not be morally good.
Gist of Idea
Motives decide whether an action is good, and what is done decides whether it was right
Source
W. David Ross (The Right and the Good [1930], §VII)
Book Reference
Ross,W.David: 'The Right and the Good' [OUP 1930], p.156
A Reaction
This sounds neat, but it is hard to find clearcut examples to confirm it. Having your cat put down may be right but not good, but presumably your motive was good.