Albert Barnes Commentary Exodus 23:18

"Thou shalt not offer the blood of my sacrifice with leavened bread; neither shall the fat of my feast remain all night until the morning." — Exodus 23:18 (ASV)

The blood of my sacrifice - It is generally considered that this must refer to the Paschal Lamb. See Exodus 12:7, Exodus 12:11, Exodus 12:13, Exodus 12:22–23, Exodus 12:27.

The fat of my sacrifice - Strictly, the fat of my feast; the best part of the feast, that is, the Paschal lamb itself. Compare Exodus 34:25.