Midrash su Isaia 43:26

(Lev. 9:2:) “Then he said unto Aaron, ‘Take a calf [of the herd for a sin offering].’” Why was it not told him [to take] a bull instead of a calf? He said to him, “Because through the calf (of Exod. 32) the priesthood was shaken in your hand, through a calf it is being established in your hand.” And not only that, but lest Israel say there are sins [clinging] to them from the deed of the calf, for that reason He said they should offer a calf [for a sin offering]. Thus it is stated (in Lev. 9:3), “And you shall speak unto the Children of Israel, saying, ‘Take a male goat for a sin offering and a calf….’” [These things were said] so that they would know that they had been forgiven for the deed of the calf. The Holy One, blessed be He, said to them, “In this world, they have been forgiven through offerings, but in the world to come I will wipe away their sins without an offering.” It is so stated (in Is. 43:25), “I, even I, will pardon¹²Mohel; cf. the Masoretic Text which reads moheh (“wipe away”). your transgressions for My own sake and will not remember your sins.”

All of those seven days that Moshe was occupied with the tabernacle, he was sprinkling the blood and incinerating the fats. The Holy One, blessed be He, said to him, "What do you think, call to your brother [so that he will do it from now on]." Hence it is written, Moshe called to Aharon and to his sons and to the elders of Israel” – so as to aggrandize him in front of the elders. The Holy One, blessed be He, said to him, "Call the elders and appoint him in front of them, that they not say, 'He became high priest on his own.'" "Take for yourself a young calf" – and why did He not say, "A bull?" But rather, the priesthood was made doubtful in your hand with a calf, [so too,] is it established in your hand with a calf. And not only that, but [so] that Israel not say, "The sins from the event of the golden calf are [still] ours." Hence they should also offer a calf, as it is stated, "And to the Children of Israel speak, saying, 'Take a male goat for a sin-offering and a calf and a lamb that are a year old'" - so that they would know that they underwent atonement for the event of the calf. The Holy One, blessed be He, said, "In this world, they underwent atonement with a sacrifice; and in the world to come, I pardon your transgressions without a sacrifice, as it is stated (Isaiah 43:25), 'I, I am the One that wipes away your transgressions for My sake.'"