Quotations about:
    praying

He who sings, prays twice.

[Qui cantat, bis orat.]

Augustine of Hippo (354-430) Christian church father, philosopher, saint [b. Aurelius Augustinus]

(Spurious)

Sometimes cited to Sermon 336, but this text is not found  there. Often given as "Qui bene cantat bis orat" (properly, "He who sings well prays twice.")

The closest found in Augustine's work (CCL 39, per here) is:

For he who sings praise, does not only praise, but also praises joyfully; he who sings praise, not only sings, but also loves Him whom he is singing about/to/for. There is a praise-filled public proclamation in the praise of someone who is confessing/acknowledging God, in the song of the lover there is love.

[Qui enim cantat laudem, non solum laudat, sed etiam hilariter laudat; qui cantat laudem, non solum cantat, sed et amat eum quem cantat. In laude confitentis est praedicatio, in cantico amantis affectio.

Alternate:

The one who sings praise, not only praises, but also praises joyfully; the one who sings praise, not only sings, but also loves Him for whom he sings. In the praise by one who confesses the Divine Being, praise actually is a public profession; and in the song of the lover is affection for the Beloved.

But that's still not the simplified version, even in meaning, that is the subject matter here.

The earliest I could find the Latin, Qui cantat, bis orat, was in Wenzel Nicolaides, Cantiones Evangelicae: Ad Usitatas Harmonias (1554).

For more discussion, see here:

• Augustine: He who sings prays twice | They didn't say it.
• St. Augustine: “He who sings prays twice” | Fr. Z's Blog.