
“In necessary things, unity; in doubtful things, liberty; in all things, charity (love).”
In necessariis unitas, In dubiis libertas, In omnibus autem caritas.
The first known occurence of such an expression is as "Omnesque mutuam amplecteremur unitatem in necessariis, in non necessariis libertatem, in omnibus caritatem" in De Republica Ecclesiastica by Marco Antonio de Dominis, Pars I. London (1617), lib. 4 cap. 8 p. 676 (penultimate sentence) books.google http://books.google.de/books?id=QcVFAAAAcAAJ&pg=PA676, cf. liberlocorumcommunium http://liberlocorumcommunium.blogspot.com/2010/03/in-necessariis-unitas-in-non.html.
Misattributed