[IULIANUS libro tertio ad Urseium Ferocem. ] §19.1.28.prPraedia mihi uendidisti et conuenit, ut aliquid facerem: quod si non fecissem, poenam promisi.
[JULIANUS, On Urseius Ferox, Book III.] You sold me tracts of land and it was agreed that I should do something; and if I did not do it, I promised a penalty.
respondit, uenditor antequam poenam ex stipulatu petat, ex uendito agere potest: si consecutus fuerit, quantum poenae nomine stipulatus esset, agentem ex stipulatu doli mali exceptio summouebit: si ex stipulatu poenam consecutus fueris, ipso iure ex uendito agere non poteris nisi in id, quod pluris eius interfuerit id fieri.
He answered: before the seller claims the penalty under the stipulation, he can sue on the sale. If he has obtained as much as was stipulated under the name of penalty, the plea of fraud will bar him if he sues under the stipulation. If you (the seller) have obtained the penalty under the stipulation, you cannot by operation of law sue on the sale, except for the amount by which it was of greater interest to him that the thing should be done.