Midrasch zu Wajikra 16:18

7) (Vayikra 16:18) ("And he shall go out to the altar which is before the L–rd, and make atonement upon it. And he shall take of the blood of the bullock and of the blood of the he-goat, and he shall place it upon the corners of the altar roundabout.") "And he shall go out to the altar which is before the L–rd": What is the intent of this? (i.e., Is he not already standing in the sanctuary, where the golden altar is found?) R. Nechemiah answered: Because we find in respect to the bullock that is brought for all the mitzvoth (i.e., the bullock of the anointed priest) that the Cohein stands outside (i.e., at the far end of) the altar and sprinkles upon the curtain, I might think that the same applies here. It is, therefore, written "And he shall go out to (the far end of) the altar." Where was he, (then, until now)? On the inside of the altar (before the curtain).

8) — But perhaps we are speaking of the outer altar (that he goes out to from the sanctuary)! (This is not to be entertained, for) it is written "which is before the L–rd," which can apply only to the inner altar.

9) "and he shall make atonement upon it (the altar)": atonement which is (made) upon its body. (i.e., atonement through the blood, which is placed upon the corners of the altar [and not verbal atonement])."and he shall take of the blood of the bullock and of the blood of the he-goat": intermixed. I might think of each by itself; it is, therefore, written (Shemoth 30:10) "of the blood of the sin-offering of the atonement once a year." How, then, am I to understand "and he shall take of the blood of the bullock and of the blood of the he-goat"? As "intermixed." (For otherwise, it would be twice a year.)