John Gill Commentary Exodus 34:26

"The first of the first-fruits of thy ground thou shalt bring unto the house of Jehovah thy God. Thou shalt not boil a kid in its mother`s milk." — Exodus 34:26 (ASV)

The first of the firstfruits of your land you shall bring ,
&c.] This, and another law in this verse, concerning not boiling a kid in his mother's milk, are repeated from (Exodus 23:19) . (See Gill on Exodus 23:19).