§1. The judge can accept an oral petition whenever the petitioner is impeded from presenting a libellus or the case is easily investigated and of lesser importance.
§2. In either case, however, the judge is to order the notary to put the act into writing; the written record must be read to and approved by the petitioner and has all the legal effects of a libellus written by the petitioner.
Source: Code of Canon Law (Vatican.va)