95 Yoma 1/1-4

(1) Seven days before the Day of Atonement, we sequester the High Priest from his house to the Palhedrin Chamber, and we prepare for him another priest in his place, [for] perhaps there will occur in him a disqualification. Rabbi Yehuda says: We even prepare another wife for him, [for] perhaps his wife will die; as it is said, "and he shall atone for himself and for his household" - his "household" is his wife. The Sages said: If so, there is no end to the matter.

(2) All seven days [of his sequestration], [the High Priest] casts the blood, and burns the incense, and cleans the lamps, and offers the head and the leg [of the continual-offering]. All other days, if he wants to offer, he offers — for the High Priest offers a portion first, and takes a portion first.

(3) They provided for him elders from the elders of the [high] court who would read before him the order of the service [for Yom Kippur]. They would say to him: My master the High Priest, memorize the order of the service; perhaps you forgot or never learned. On the day before Yom Kippur in the morning they stood him in the eastern gate of the Temple and passed before him all the bulls, rams and lambs [that would be used the next day in the service] so that he would recognize and be familiar with the service [of offering each of them].

(4) All seven days, they would not prevent him from eating or drinking. The day before Yom Kippur, toward nightfall, they would not let him eat a lot, because food brings on sleep.