Yenghe hatam is one of the four formulas (the other three being Ashem Vohu, Ahuna Vairya and Airyaman ishya) of the Gathic canon, that is, part of the group of texts composed in the more archaic dialect of the Avestan language.
Other texts on the religion of Ahura Mazda
http://www.zoroastrian.org/GathaSongs/supplements2.htm http://www.zoroaster.com/References
Yenghe hatam Wikipedia(Text) CC BY-SA