Eleutherius of Tournai (d. 532) Eleutherius Tornacensis
https://en.wikipedia.org/wiki/Eleutherius_of_Tournai

Corpus Corporum
Works by Eleutherius Tornacensis
http://www.mlat.uzh.ch/MLS/?viaf=264992460
SERMO, SEU CONFESSIO DE SS. TRINITATE.
http://www.mlat.uzh.ch/MLS/xfromcc.p...current_title=

Migne Latina PL 65, col 85-86 [86C]
https://books.google.com/books?id=zBERAAAAYAAJ&pg=PA85

Documenta Catholica Omnia
http://www.documentacatholicaomnia.eu/04z/z_0456-0531__Eleutherius_Tornacensis__Epistolae__MLT.pdf. html

SERMONES S. ELEUTHERII.(1847)
SERMO, SEU rO.NFESSIO DE SS. TRINITATE.
https://books.google.com/books?id=zBERAAAAYAAJ&pg=PA83

“S. Fulgentii, episcopi Ruspensis, Felicis IV et Bonifacii II summorum Pontificum, SS. Eleutherii et Remigii Tornacensis Remensisque episcoporum, Prosperi ex Manichaeo conversi, Montani episcopi Toletani,” opera omnia: ex memoratissimis editionibus Mangeantii, Mansi, Gallandii, Margarini de la Bigne, Francisci de Lorenzana diligenter expressa (1861)
https://books.google.com/books?id=cZ_BTx1JJMoC&pg=PA85
I John 5 7 : Eleutherius (456-487 AD) : Bishop of Tournai : Sermon, Confession of SS. Trinity : CITATION

(0086C) Tres quidem sunt qui testimonium dant in coelo, Pater, Verbum et Spiritus sanctus: hi tres unum sunt.

(0086C) have three that bear record in heaven, the Father, the Son and the Holy Ghost are three in one.

===SOURCE:
Sermons, Seu Confessio De SS. Trinitate

Et ideo, licet dicatur quod per hominem facta est resurrectio mortuorum, tamen intelligere debetis hominem factum, verbum quod ex Deo est, et per eum mortis imperium esse destructum. Ut autem Scriptura attestatur, Veniet novissimis temporibus unus Filius et Dominus in gloria Patris, ut iudicet orbem in aequitate. Necessarium quoque est ut credatis incarnationem Domini nostri Iesu Christi, nativitatem, circumcisionem, apparitionem, Evangelia, passionem, mortem, resurrectionem, et in coelos ascensionem. Haec est enim fides recta. Sed quoniam Deum carne unitum iuxta subsistentiam virgo concepit, virgo peperit, idcirco eam Christi genitricem profiteamini: non quod verbi natura existendi principium de carne sortita sit. Erat enim in principio Verbum, et Verbum erat apud Deum, et Deus erat Verbum: et ipse est conditor saeculorum, Pater universitatis. (0086C) Tres quidem sunt qui testimonium dant in coelo, Pater, Verbum et Spiritus sanctus: hi tres unum sunt. Igitur omnium creatorem unum in substantia, Trinitatem in personis confitemini, ut ad coelestia gaudia pervenire mereamini, ubi florent merita sanctorum, quorum gaudium et exsultatio non desinet usque in sempiternum, regnante Domino nostro Iesu Christo, cum Patre coaeterno, cooperante gratia Spiritus sancti, cui sit laus, imperium, per omnia saecula saeculorum. Amen.

===Google Translate:

Language or confession of SS. Trinity
Though it is said that the man was dead, they must understand the man came word that comes from God, and that a death sentence would be destroyed. The Scripture bears witness to come to the son of one of the last times in glory to judge the world in equity. It is also necessary to understand the incarnation of our Lord's birth, circumcision, an appearance on the Gospel, the passion, death, resurrection and ascension into heaven. For this is correct. But because it is united to the flesh, God, according to the subsistence of a virgin should conceive and she gave birth to a virgin, the Mother of Christ and profess this reason, it up: it is not because of the word of the nature of the beginning of the existence of the flesh, let all lots. In the beginning was the Word, and the Word was with God and the Word was God and he is the founder of the world, father of the corporation. (0086C) have three that bear record in heaven, the Father, the Son and the Holy Ghost are three in one. Therefore, the Creator of all art One in Being, and Three in persons, and give glory, so as to heavenly things, the joys of found worthy to come, where, in bloom, the merits of the saints, whose joy, and exultation, would not cease to be great forever, the reign of the Lord our Lord Jesus Christ, with the Father, co-eternal, co-operation of the grace of the Holy Spirit, to whom the let there be praise, and the government, in all things, world without end. Amen.
Historically, the question of the authenticity of the specific Sermons as being by Eleutherius was brought up by:

Alban Butler (1710-1773)
http://en.wikipedia.org/wiki/Alban_Butler

As in this notation in:

The Lives of the Fathers, Martyrs and Other Principal Saints: Compiled from Original Monuments and Other Authentic Records; Illustrated with the Remarks of Judicious Modern Critics and Historians, Volume 2 (1866)
https://books.google.com/books?id=ZVs3AAAAMAAJ&pg=PA169
https://www.bartleby.com/210/2/203.html

ST. ELEUTHERIUS, MARTYR.
BISHOP OF TOURNAY
A.D. 632.
He was bom at Toumay, of Christian parents, whose family had been converted to Christ by St. Piat, one hundred and fifty years before. The faith had declined at Tornay ever since St. Piat’s martyrdom, by reason of its commerce with the heathen islands of Taxandria, now Zeland, and by means of the heathen French kings, who resided some time at Toumay. Eleutherius was chosen bishop of that city, in 486; ten years after which King Clovis was baptized at Rheims. Eleutherius converted the greater part of the Franks in that country to the faith, and opposed most zealously certain heretics who denyed the mystery of the Incarnation, by whom he was wounded on the head with a sword, and died of the wound five weeks after, on the first of July, in 532. The most ancient monuments, relating to this saint, seem to have perished in a great fire which consumed his church, and many other buildings, at Toumay, in 1092, with his relics. See Mineus, and his life written in the ninth century, extant in Bollandus, p. 187.* Of the sermons ascribed to St Eleutherius, in the Library of the Fathers, t. 8. none seem sufficiently warranted genuine, except three on the Incarnation and Birth of Christ, and the Annunciation, See Dom Rivet, Hist. Liter, t. 3. p. 154, and t. 5. p. 40, 41. Galia Christ. Nova, t. 3. p. 571. and Henschenius, p. 180.

and he was referencing older studies, including one by:

Godfrey Henschen (1601-1681)
https://en.wikipedia.org/wiki/Godfrey_Henschen

and an early volume, likely #1, of the

Histoire littéraire de la France

https://en.wikipedia.org/wiki/Histoire_litt%C3%A9raire_de_la_France

written by:

André Riveto (1572-1651)
https://en.wikipedia.org/wiki/André_Rivet.

Nothing is specified as to any negatives in our Sermon on confessing the Trinity, and there are no visible problems in the work being early 500s. Or its being by Eleutherius, and its being in volumes that include the learned Fulgentius.

On the plus side, there is a very strong reference , where S. A. Bennett, BA, of Lincoln's Inn says there is a specific indication of this Trinity sermon being presented to Symmachus in 512 AD.

A Dictionary of Christian Biography, Literature, Sects and Doctrines: Being a Continuation of 'The Dictionary of the Bible (1880)
https://books.google.com/books?id=qGsvAQAAIAAJ&pg=PA78

The following writings have been assigned to him: Sermo, seu Confessio dc SS. Trinitate, said to have been presented by him to pope Symmachus in the fourteenth year of his episcopate
(pope) Symmachus
https://en.wikipedia.org/wiki/Pope_Symmachus
Pope Symmachus (d. 19 July 514) was Pope from 22 November 498 to his death in 514. His tenure was marked by a serious schism over who was legitimately elected pope by the citizens of Rome.

Eleutherus of Tournai
Paola Marone

https://www.academia.edu/15059822/Eleutherus_of_Tournai

He also went to 'Rome, first to Pope Symmachus and then to Pope Hormisdas, and held a synod in 527. Died 30 August 531. Six sermons (Sermo, seu confessio de SS. Trinitate; Transitus S. Eleutherii episcopi; Sermo de Trinitate; Sermo de incamatione Domini; Sermo de natale Domini; Sermo in annuntiationis festum) and a prayer (Oratio Beati Eleutherii) have been erroneously attributed to Eleutherus.

CPL 1004; PL 65, 83-102; P. Rutland, Les Monumenla hisloriae Tomacensis saec. XII: Annuaire de (’Academic Royale d’Archeologie de Belgique 73 (1926) 255-313; Id., Les origines legendaires de Tournai: RBPli 25 (1946-1947) 555-581; A. Lumpe, Die Quellen von Ps. Eleutherius, sermo de Trinitate: RhM 100 (1957) 199-200; BS IV, 1012; DHGE XV, 150-153; Patrologia IV, 300.
Adolf Lumpe
Die Quelle von Pseudo-Eleutherius, Sermo de trinitate 1 (1957) - AVAILABLE ONLINE
https://www.jstor.org/stable/4124404...n_tab_contents
(here it is hard to see)
http://www.rhm.uni-koeln.de/100/M-Lumpe.pdf

004 Berardino Patrologia I Padri Latini Dal Concilio Di Calcedonia 451 A Beda Vol 4 Marietti 1996
Eleutherius di Tournai
https://archive.org/details/004Berar...6Pdf/page/n301