Full Idea
If a man should give to his neighbour a potion which he really believes will poison him, but which, in the event, proves salutary, and does much good; in moral estimation, he is a poisoner, and not a benefactor.
Gist of Idea
If an attempted poisoning results in benefits, we still judge the agent a poisoner
Source
Thomas Reid (Essays on Active Powers 3: Princs of action [1788], 5)
Book Reference
Reid,Thomas: 'Inquiry and Essays', ed/tr. Beanblossom /K.Lehrer [Hackett 1983], p.319
A Reaction
I take Reid to mean that morality concerns how we assess the agent, and not the results of his actions. Mill and Bentham concede that we judge people this way, but don't think morality mainly concerns judging people.