Excusationum liber singularis
Dig. 27,1,7Ulpianus libro singulari excusationum. Paupertas sane dat excusationem, si quis imparem se oneri iniuncto possit probare, idque divorum fratrum rescripto continetur.
Ulpianus, On Excuses. Poverty, indeed, affords a good excuse, where anyone can prove that he is unequal to the burden imposed upon him; and this is contained in a Rescript of the Divine Brothers.