The Catholic faith
Eastern churches
A ‘Confession of Sins’
Каюсь, Господи, помилуй и прости.

Another excerpt from The Way of a Pilgrim (buy the book)
Intense! Must be read in context so you don’t lose your mind. I’m actually not a devoté of the Jesus Prayer — it’s a practice of Orthodox* monks and nuns — but Pilgrim is a lovely book all the same.

*There is a new book pick (for sale) on this page by Adrian Fortescue thanks to Dr Philip Blosser.