Dvadasaha
Dvādaśāha – (Sanskrit: द्वादशाह) literally means the twelve-day sacrifice. The "Soma sacrifice" that takes twelve-days is called "Dvādaśāha" in which a ten-day sequence called "dāśa-rātra", is flanked by two intensive day and overnight sacrifices called "atirātras" as opening and closing days. The "Agnistoma" serves as the paradigm for all "Soma sacrifices" up to those of twelve days duration, the "Dvādaśāha" soma sacrifice is paradigmatic for "Soma sacrifices" of twelve days and more. The Aitareya Brahmana and the Kausitaki Brahmana, belong to the Rig Veda, both preserve this Rig Vedic rite. The Aitareya Brahmana (IV.25) calls the  Dvādaśāha sacrifice as the 'sacrifice of Prajapati', and the Jaiminiya Brahmana (III.302) calls the stomas of "Dvādaśāha" as the 'powerful sons of Prajapati'. The twelve-days "Soma sacrifices" are called "Ahinas", and the longer ones are called "Sattras". The Aitreya Brahmana describes the "Dvādaśāha sacrifice" in its Pancika IV.iv.23 to V.iv.25, beginning with the origin and the initial ritual of this sacrifice. The first six "Prishtha" days of the "Dvādaśāha " sacrifice represent the mouth, the "Chandomah" days are the seventh to the ninth which represent what is in the mouth as tongue palate and teeth; but that by which one  produces articulate sounds of speech or by which one distinguishes sweet and not sweet, is the tenth day which is the 'day of happiness'. Those desirous of prosperity perform this ritual. The fundamental scheme of the sattras is that of a "Dvādaśāha" comprising a "prayaniya-atiratra" (one day), a "prishthaya-shada-aha" (six days), "chandomas" (three days), an "avivakya" (one day) and an "udayaniya-atiratra" (one day), which programme can be suitably extended. The "Dvādaśāha" sacrifice is both, "Ahina" and "Sattra" types of "Soma sacrifice", the former is "Vyudha", and the latter, "Samudha". In the "Sattra" type of session, there  is no sacrifice, only Brahmins perform this ritual. In this context, Badarayana states:- Shankara explains that when a liberated soul wishes to have a body, he gets one; and when he desires to remain without it, he has none; for his will is true and desires are diverse like the "Dvādaśāha" which can be both a "sattra" and an "ahina", because of the injunction about the sacrifice itself and the specification of the sacrificer. And, Gambhirananda clarifies that "Dvādaśāha" becomes "Ahina" when there is injunction about it along with the specification of its performer; it is "Sattra" when it is  resorted to by many performers.