Zartosht no-diso, or Zarthost no deeso, is an important day of mourning in the Zoroastrian religion. It is a commemoration of the death anniversary of the prophet

Prophet

In religion, a prophet, from the Greek word προφήτης profitis meaning "foreteller", is an individual who is claimed to have been contacted by the supernatural or the divine, and serves as an intermediary with humanity, delivering this newfound knowledge from the supernatural entity to other people...

 Zoraster. It is observed on the 11th day (Khorshed) of the 10th month (Dae). In the seasonal calendar, Zarthost No-Diso falls on December 26th.

It is an occasion of mourning with lectures and discussions held on the life and works of the prophet

Zoroaster

Zoroaster , also known as Zarathustra , was a prophet and the founder of Zoroastrianism who was either born in North Western or Eastern Iran. He is credited with the authorship of the Yasna Haptanghaiti as well as the Gathas, hymns which are at the liturgical core of Zoroastrianism...

. Special prayers are recited, and attendance at the fire temple

Fire temple

A fire temple in Zoroastrianism is the place of worship for Zoroastrians. Zoroastrians revere fire in any form. In the Zoroastrian religion, fire , together with clean water , are agents of ritual purity...

 is very high. A much higher number of mobeds are brought to pray at the Atash Behram

Atash Behram

An Atash Behram is the highest grade of a fire that can be placed in a fire temple. The establishment and consecration of this fire is the most elaborate than all the other grades of fire...

s and Atash Adarans.

However, Zoroaster’s death is not mentioned in the Avesta

Avesta

The Avesta is the primary collection of sacred texts of Zoroastrianism, composed in the Avestan language.-Early transmission:The texts of the Avesta — which are all in the Avestan language — were composed over the course of several hundred years. The most important portion, the Gathas,...

. Nonetheless, in the Shahnama 5.92, he is said to have been murdered at the altar by the Turan

Turan

Tūrān is the Persian name for Central Asia, literally meaning "the land of the Tur". As described below, the original Turanians are an Iranian tribe of the Avestan age. As a people the "Turanian" are one of the two Iranian peoples both descending from the Persian Fereydun but with different...

ians in the storming of Balkh

Balkh

Balkh , was an ancient city and centre of Zoroastrianism in what is now northern Afghanistan. Today it is a small town in the province of Balkh, about 20 kilometers northwest of the provincial capital, Mazar-e Sharif, and some south of the Amu Darya. It was one of the major cities of Khorasan...

.