Nicaea alone is the sufficient confession of the Triune faith
Athanasius is closing his letter to the African bishops, urging them to hold only the faith confessed at Nicaea, which he says overthrows every heresy, including those who call the Holy Spirit a creature.
But let only the faith confessed at Nicaea by the Fathers hold sway among you. In that council, as we said before, all the Fathers were present—even those now fighting against it—and they signed. So the Apostle may say about us: “I praise you because you remember me in everything and hold firmly to the traditions just as I handed them on to you” (1 Corinthians 11:2). For this council at Nicaea is truly an inscription set up against every heresy. It also overthrows those who blaspheme against the Holy Spirit and call the Spirit a creature. For after the Fathers spoke about faith in the Son, they immediately added: “We believe also in the Holy Spirit,” so that by confessing a complete and full faith in the Holy Trinity they might make known in this the imprint of faith in Christ and the teaching of the Catholic Church. For it is clear both among you and among all people, and no Christian would hold a doubtful mind about this: our faith is not in creation, but in one God, the Father Almighty, maker of all things visible and invisible; and in one Lord Jesus Christ, his only-begotten Son; and in one Holy Spirit—one God known in the holy and perfect Trinity. Baptized into this Trinity and being joined to the divinity in it, we believe that we will also inherit the kingdom of heaven in Christ Jesus our Lord, through whom to the Father be glory and might forever. Amen.
Greek
Ἀλλὰ μόνον κρατείτω ἐν ὑμῖν ἡ ἐν Νικαίᾳ παρὰ τῶν Πατέρων ὁμολογηθεῖσα πίστις· ἐν ᾗ καὶ πάντες καὶ τῶν νῦν μαχομένων πρὸς αὐτὴν παρῆσαν Πατέρες, καθὰ προείπομεν, καὶ ὑπέγραψαν· ἵνα καὶ περὶ ἡμῶν ὁ Ἀπόστολος εἴπῃ· Ἐπαινῶ δὲ ὑμᾶς, ὅτι πάντα μου μέμνησθε, καὶ καθὼς παρέδωκα ὑμῖν τὰς παραδόσεις, οὕτω κατέχετε. Αὕτη γὰρ ἡ ἐν Νικαίᾳ σύνοδος, ἀληθῶς στηλογραφία κατὰ πάσης αἱρέσεώς ἐστιν. Αὕτη καὶ τοὺς βλασφημοῦντας εἰς τὸ Πνεῦμα τὸ ἅγιον, καὶ λέγοντας αὐτὸ κτίσμα, ἀνατρέπει. Εἰρηκότες γὰρ οἱ Πατέρες περὶ τῆς εἰς τὸν Υἱὸν πίστεως, ἐπήγαγον εὐθύς· Πιστεύομεν καὶ εἰς τὸ Πνεῦμα τὸ ἅγιον, ἵνα, τελείαν καὶ πλήρη τὴν εἰς τὴν ἁγίαν Τριάδα πίστιν ὁμολογήσαντες, τὸν χαρακτῆρα τῆς ἐν Χριστῷ πίστεως, καὶ τὴν διδασκαλίαν τῆς Καθολικῆς Ἐκκλησίας ἐν τούτῳ γνωρίσωσι. Δῆλον γὰρ καὶ παρ' ὑμῖν καὶ παρὰ πᾶσι καθέστηκε· καὶ οὐδεὶς ἂν Χριστιανῶν ἀμφίβολον εἰς τοῦτο σχοίη τὴν διάνοιαν, ὡς οὐκ ἔστιν ἡμῶν ἡ πίστις εἰς τὴν κτίσιν, ἀλλ' εἰς ἕνα Θεὸν Πατέρα παντοκράτορα, πάντων ὁρατῶν τε καὶ ἀοράτων ποιητήν· καὶ εἰς ἕνα Κύριον Ἰησοῦν Χριστὸν, τὸν Υἱὸν αὐτοῦ τὸν μονογενῆ· καὶ εἰς ἓν Πνεῦμα ἅγιον· ἕνα Θεὸν τὸν ἐν τῇ ἁγίᾳ καὶ τελείᾳ Τριάδι γινωσκόμενον· εἰς ἣν καὶ βαπτιζόμενοι, καὶ ἐν ταύτῃ συναπτόμενοι τῇ θεότητι, πιστεύομεν καὶ κληρονομῆσαι βασιλείαν οὐρανῶν ἐν Χριστῷ Ἰησοῦ τῷ Κυρίῳ ἡμῶν, δι' οὗ τῷ Πατρὶ ἡ δόξα καὶ τὸ κράτος εἰς τοὺς αἰῶνας. Ἀμήν.