"Vere dignum et iustum est, æquum et salutare, nos tibi semper et ubique gratias agere. . . ."
Truly fitting and just [it] is, [truly] equitable and salutary, that we to you everywhere and always give thanks. . . .
The opening words of every Preface in the current Missale Romanum, and of Catholic Prefaces from time immemorial. A possibly abbreviated form of the whole ("Uere dignum") is present in the Prefaces of the early 7th-, but possibly even 6th-, or 5th-century "Leonine" or Veronese Sacramentary, though E. J. Yarnold, on p. 231 of the revised edition of The study of liturgy, citing p. 202 of the Sacramentarium Veronense as edited by Mohlberg in 1956, refers to "A fourth-century fragment of an Arian polemical work [that] quotes from two such Catholic prefaces", the first of which begins simply "it is worthy and just for us here and everywhere to give you thanks, holy Lord, almighty God [(Dignum et iustum est nos tibi hic et ubique gratias agere)]", an indication that "Vere dignum" may have been not an abbreviation, but an expansion on an older form ("Dignum et iustum est") that did not include "æquum et salutare" or even "Vere". (In endnote no. 10 on p. 242 Yarnold cites two reconstructions of this early Canon of A.D. 378-416, one by Vagaggini (Canon of the Mass and liturgical reform (1967), pp. 31-32), and another in Prayers of the Eucharist: early and Reformed, ed. Jasper & Cuming, 3rd edition (1987), pp. 155-158, which begins on p. 156 with the words, "It is fitting and right, it is just and right, that we should give you thanks for all things. . . .") The longer form inclusive of both "Vere" and "æquum et salutare" occurs at least 5 times in the mid-8th-century Gelasian, and at least 20 in the 8th/9th-century Gregorian. (I am only shooting just quickly from the hip here, being unfamiliar with the literature except as cited by Yarnold.)