I have not found this Latin text translated into English anywhere, so I've given it my best shot. This is Pope St. Leo professing, in AD 447, that the Church's catholic faith professes, among other things, that the Holy Spirit proceeds from both the Father and the Son. It comes from Quam laudabiliter, which can be found in the 1957 Latin Denzinger compilation, n. 284.
Primo itaque capitulo demonstratur,
quam impie sentiant de Trinitate divina,
qui et Patris et Filii et Spiritus Sancti unam atque eandem asserunt esse personas,
tamquam idem Deus nunc Pater,
nunc Spiritus Sanctus nominetur;
Thus, in the first chapter it was demonstrated,
how irreverently they think about the Holy Trinity,
who claim the Father and the Son and the Holy Spirit to be one and the same persons,
as if the same God is now called Father,
[and] now called Son,
[and] now called the Holy Spirit;
nec alius sit qui genuit,
alius qui genitus est,
alius qui de utroque processit,
sed singularis unitas in tribus quidem vocabulis,
sed non in tribus sit accipienda personis.
not even that They are the One Who begets,
the Other Who was begotten,
the Other Who proceeded from both,
yet a singular unity, in three names to be sure,
but not be understood in three persons.
Quod blasphemiae genus de Sabellii opinione sumpserunt,
cuius discipuli etiam Patripassiani merito nuncupantur;
Concerning the blasphemy they took up, its origin is of the beliefs of Sabellius,
whose disciples, furthermore, are rightly called "Patripassionists;"
quia si ipse est Filius qui et Pater,
crux Filii Patris est passio;
because if the very person is the Son who is [also] the Father,
the crucifixion of the Son is the passion of the Father;
et quidquid in forma servi Filius Patri oboediendo sustinuit,
totum in se Pater ipse suscepit.
and whatsoever the Son, in the form of a slave to the Father Who must be obeyed, sustained,
the Father Himself took up all of it in Himself.
Quod catholicae fidei sine ambiguitate contrarium est,
quae Trinitatem deitatis sic homousion confitetur,
ut Patrem et Filium et Spiritum Sanctum sine confusione indivisos,
sine tempore sempiternos,
sine differentia credat aequales:
Which is contrary, without ambiguity, to the Catholic faith,
which confesses the Blessed Trinity of the divine nature homousion in this manner,
that she believes the Father and the Son and the Holy Spirit [are] indivisible without confusion,
eternal without time,
equal without difference:
quia unitatem in trinitate non eadem persona,
sed eadem implet essentia.
because not the same person fulfills the unity in the Blessed Trinity,
but the same essence (substance).