CELEBRET. – Certificate issued by the competent ecclesiastical authority, attesting that a priest may celebrate Mass. It states the holder’s name, the date, the time limit, the diocesan or institute seal, together with the signature of the Ordinary if the priest is secular, or of the superior if he is religious. For a priest of an Eastern rite, a certificate from the S. Congregation for the Oriental Churches is sufficient.
There are two cases in which the parish priest or rector of a church may authorize a visiting priest to say Mass
without the c.: 1) when the priest is known to him to be of unquestionable probity; 2) if the priest is unknown, he may permit the celebration only once or twice, provided that the priest wears ecclesiastical dress, accepts no stipend, and signs a special register, indicating his office and the diocese to which he belongs (can. 804).