The Khordeh Avesta, or "The Little Avesta," is the sacred book of the Zoroastrians. However, Zarathushtra was a poet-prophet. He composed sacred hymns known as the "Gathas", and his teachings were handed down orally through the priesthood. It is believed that Alexandar destroyed a lot of the written teachings and massacred Zoroastrian priests during the seige of Persepolis. All that remains is the Khordeh Avesta.
But here's something that may not be found in any holy book. It's what my aunt told me years ago, and the simplicity of the image has stayed with me to this day:
Our prayers travel upwards in the form of rays of light. If the prayer is genuine, it is intercepted by an angel who is specially trained to answer prayers. The strength of the beam of light depends entirely on the sincerity and selflessness of the prayer.
I love the idea of angels roaming the heavens, watching over Earth, responding to light that, for a change, comes from us.