When it is said
The priest said it for everyone present. Its words fit one person praying alone just as well.
It suits a time when unkind things are being said about you, and a time when flattery tempts you.
Where it comes from
No author known
A Mass against slanderers
The prayer opens a Mass headed “against those who speak ill of us” in the Gelasian Sacramentary, a book of Roman Mass prayers. The book was put together near Paris around AD 750 from older material that came from Rome. The same prayer opens the Mass against slanderers in the Gregorian book the Franks used under Charlemagne.
H. A. Wilson, The Gelasian Sacramentary (Oxford, 1894), on archive.org; The Cult of Saints in Late Antiquity database, University of Oxford, record E07005; H. A. Wilson, The Gregorian Sacramentary under Charles the Great (1915), on archive.org
Our good name
An older book of Roman Mass prayers, the Leonine Sacramentary, survives in a manuscript at Verona written early in the 600s. It has the first half of this prayer with a different ending. Beside it stands a second prayer, asking that we look past the lies of the wicked and follow what will help our conscience and our good name.
C. L. Feltoe, Sacramentarium Leonianum (1896), on archive.org
In Latin
Praesta, quaesumus, Domine, ut mentium reprobarum non curemus obloquium,
sed eadem pravitate calcata
exoramus ut nec terreri nos lacerationibus pateris iniustis,
nec captiosis adulationibus implicari,
sed potius amare quae praecipis. Per.
From H. A. Wilson, The Gelasian Sacramentary (Oxford, 1894), pages 279 and 280.