|Three times each year...|
See note on Exodus 23:14.
|Master of the Universe|
|Do not sacrifice...|
See Exodus 34:25, Deuteronomy 16:4.
This was the part that was to be burned on the altar. See Leviticus 3:16, 17:6. Also see Exodus 29:13, Leviticus 3:3, 7:31, etc.
Or, 'festival offering' (see Chagigah 10b). See Exodus 34:25, Deuteronomy 16:4. This is speaking specifically of the Passover offering (Rashbam), but applies to all offerings and sacrifices (Sefer HaMitzvoth, Negative Commandment 116). Above (Exodus 12:10), there was a commandment not to leave over the edible portions; here there is a commandment not to leave over the portions that are to be burned on the altar.