פּירוש אויף יחזקאל 44:27

“On the day that he reenters the sanctuary” [44:27]. The first time the priest will bring sacrifices in the Temple, he should bring a sin offering.

And on the day that he enters into the Sanctuary for the first time to initiate himself into the service, he shall offer up his sin-offering; this is his one tenth of an ephah [of flour]. In Moed Katan (16a) the following is taught: the regular priest requires one tenth of an ephah on the day of his initiation, as it is stated (Lev. 6:13): “This is the offering of Aaron and his sons, etc.” and as is explained in Tractate Menachoth (51b).