[POMPONIUS libro sexto ad Sabinum. ] §13.7.2.prSi debitor rem pignori datam uendidit et tradidit tuque ei nummos credidisti, quos ille soluit ei creditori, cui pignus dederat tibique cum eo conuenit, ut ea res, quam iam uendiderat, pignori tibi esset, nihil te egisse constat, quia rem alienam pignori acceperis: ea enim ratione emptorem pignus liberatum habere coepisse neque ad rem pertinuisse, quod tua pecunia pignus sit liberatum.
[POMPONIUS, on Sabinus, Book VI] If a debtor has sold and delivered a thing given as a pledge, and you have lent him money, which he has paid to that creditor to whom he had given the pledge, and it has been agreed between you and him that that thing, which he had already sold, should be a pledge to you, it is established that you have effected nothing, because you have accepted another's property as a pledge: for by that reasoning the buyer began to hold the pledge freed, and it was of no relevance that the pledge was freed by your money.