[GAIUS libro tertio ad edictum prouinciale. ] §3.5.2.prSi quis absentis negotia gesserit licet ignorantis, tamen quidquid utiliter in rem eius impenderit uel etiam ipse se in rem absentis alicui obligauerit, habet eo nomine actionem: itaque eo casu ultro citroque nascitur actio, quae appellatur negotiorum gestorum.
[GAIUS, on the Provincial Edict, book 3.] If anyone has managed the affairs of an absent person, even if the latter is unaware of it, nevertheless, for whatever he has usefully expended on his property, or even if he has himself bound himself to someone else on behalf of the property of the absent person, he has an action on that account; therefore in that case an action arises on both sides, which is called the action for business managed.
et sane sicut aequum est ipsum actus sui rationem reddere et eo nomine condemnari, quidquid uel non ut oportuit gessit uel ex his negotiis retinet: ita ex diuerso iustum est, si utiliter gessit, praestari ei, quidquid eo nomine uel abest ei uel afuturum est.
And indeed, just as it is fair that he himself should render an account of his conduct and be condemned on that account for whatever he either did not manage as he ought to have done, or retains from these transactions; so on the other hand it is just, if he managed usefully, that there should be made good to him whatever on that account is either missing from him or will be missing.