Numbers 8:8

8:8 Then they are to take a young bull with its grain offering of fine flour mixed with olive oil; and you are to take a second young bull for a purification offering. ¹ 

[8:8]  ¹ sn The first sacrifice was for the purification of the Levites. The second animal, which Moses was to take, would be used for the purification of the tabernacle from all pollution.