Num 29:35-38
The eighth day was to be azereth, a closing feast, and only belonged to the feast of Tabernacles so far as the Sabbath rest and a holy meeting of the seventh feast-day were transferred to it; whilst, so far as its sacrifices were concerned, it resembled the seventh new moon’s day and the day of atonement, and was thus shown to be the octave or close of the second festal circle (see at Lev 23:36).