[ULPIANUS libro uicensimo septimo ad edictum. ] §12.2.36.prSi actor deferat iusiurandum de sola constituta pecunia et reus iurauerit, exceptione utetur, si de constituta conueniatur: sed si de sorte, id est de priore obligatione conueniatur, exceptio cessabit, nisi de hac quoque iurauerit aduersario deferente.
[ULPIANUS, Book 27 on the Edict.] If the plaintiff should tender an oath concerning only the agreed payment and the defendant has sworn, the defendant will use an exception if he is sued on the agreed payment; but if he is sued on the principal, that is, on the prior obligation, the exception will not apply, unless he has also sworn on this, with the adversary tendering the oath.