Charles Ellicott Commentary Leviticus 9:10

"but the fat, and the kidneys, and the caul from the liver of the sin-offering, he burnt upon the altar; as Jehovah commanded Moses." — Leviticus 9:10 (ASV)

But the fat ... he burnt upon the altar. —The fat portions of this sin offering Aaron was still to burn upon the altar as Moses had done before (Leviticus 8:21; Leviticus 8:28), since the miraculous fire from God did not issue forth until the burnt offering of the people was offered.