Which religious tradition preserved texts in the Avestan language?

The Avestan language was preserved by the religious tradition of Zoroastrianism.12

The texts, collectively known as the Avesta, served as the sacred scripture of the faith. Although Avestan ceased to be a spoken language around 400 BCE, it was maintained through an oral tradition by Zoroastrian priests. These texts were eventually recorded in a specialized script during the 6th century CE, under the Sasanian kings, to ensure the preservation of their liturgical and legal content.123