In necessariis unitas, In dubiis libertas, In omnibus autem caritas.

The first known occurrence 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, cf. liberlocorumcommunium.