When it is said
The service books set it for the eighth day after a baptism. The newly baptized is brought back to church, and the priest says this prayer as he loosens their belt and robe.
The Russian prayer book gives the same prayer for the anniversary of a baptism. A godparent might pray it for a godchild that day, or anyone for themselves.
Where it comes from
No author known
A prayer from the baptism service
It comes from the Orthodox baptism service in the Euchologion, the priest’s service book, and no author is named. The Great Euchologion printed in Venice in 1862 has it in Greek, among the prayers for the eighth day.
Isabel F. Hapgood, Service Book, 1906: Holy Baptism, the ablution; Euchologion to Mega, Venice 1862
The robe and the seal
Right after the baptism, the priest dresses the newly baptized in a robe and says they are “clothed with the robe of righteousness”. He then anoints them with chrism, saying each time, “The seal of the gift of the Holy Spirit.” This prayer asks God to keep that robe clean and that seal unbroken.
Isabel F. Hapgood, Service Book, 1906: Holy Baptism and Chrismation
The Scripture in it
For all of you who were baptized into Christ have clothed yourselves with Christ.
Many ask, “Who can show us the good?” Shine the light of Your face upon us, O LORD.
In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one.
And in Him, having heard and believed the word of truth—the gospel of your salvation—you were sealed with the promised Holy Spirit …
Bible text: Berean Standard Bible, public domain.
In Church Slavonic
Избавле́ние грехо́в святы́м креще́нием рабу́ Твоему́ (рабе́ Твое́й) дарова́вый,
и жи́знь па́ки рожде́ния ему́ (ей) пода́вый,
Сам, Влады́ко Го́споди,
просвеще́нием лица́ Твоего́ се́рдце его́ (ея́) озаря́ти вы́ну благоволи́;
щит ве́ры его́ (ея́) ненаве́тен соблюди́;
нетле́ния оде́жду, е́юже оде́яся, нескве́рну в нем (ней) и небла́знену сохрани́,
неруши́му в нем (ней) духо́вную печа́ть благода́ти Твоея́ соблюда́я,
ми́лостив ему́же (ейже) и нам быва́я, по мно́жеству щедро́т Твои́х.
Я́ко благослови́ся и просла́вися пречестно́е и великоле́пое и́мя Твое́,
Отца́ и Сы́на и Свята́го Ду́ха, ны́не и при́сно и во ве́ки веко́в. Ами́нь.
From the Russian prayer book on azbyka.ru, “On the anniversary of baptism”.