This is a loose translation of an alleged Venetian proverb from 1610:

To achieve justice you need
the bag of a banker,
the patience of a hermit,
to be right,
to know how to explain you are right,
to find someone who listens
and wants to acknowledge you are right,
and a debtor who can pay.

The source, a judge with a very known and brilliant blog in Spain, has it in Spanish:

Para hacer justicia hace falta
Bolsa de banquero,
Paciencia de ermitaño,
Tener razón
Saberla exponer
Encontrar quien la escuche
Y se la quiera dar
Y deudor que pueda pagar.