Deuteronomy 22:9
Thou shalt not sow thy vineyard with divers seeds: lest the fruit of thy seed which thou hast sown, and the fruit of thy vineyard, be defiled.
Cross-reference
Leviticus 19:19 gives the same prohibition against mixing seeds — a parallel law within the Torah.
James 1:6-8 condemns double-mindedness — a clear parallel to the principle against mixing seeds: both warn against mixing incompatible things.
In 2 Corinthians 6:14, Paul applies the same separation principle—do not mix—to believers and unbelievers, echoing the OT command about mixed seeds.
Matthew 6:24 teaches you cannot serve two masters — reflecting the same principle of avoiding mixture found in the seed law.
Matthew 9:16 warns against mixing old and new cloth — a similar principle of not combining unlike things.
2 Corinthians 11:3 warns against being led astray from pure devotion — a parallel to the principle of not mixing (as in seeds).
James 3:10 says praise and cursing should not come from the same mouth — a parallel to the prohibition of mixing seeds.