Incest

Xwedodah (Persian: خویدوده; khwēdōdah; Avestan: xᵛae¯tuuadaθa) is a spiritually-influenced style of consanguine marriage assumed to have been historically practiced in Zoroastrianism before the Muslim conquest of Persia.[1] Such marriages are recorded as having been inspired by Zoroastrian cosmogony and considered pious. It was a high act of worship in Zoroastrianism, and there were punishments for not performing it.[2][3] This form of direct familial incest marriage allowed Zoroastrians to marry their sisters, daughters, granddaughters, and their own mothers to take as wives.

… According to the revayats, the marriage between a mother and her son is the most superior type of xwedodah, followed by that of father and daughter, which is followed by that of brother and sister. The xwedodah becomes even more superior if the mother/daughter is also the sister of her son/father.