According to Proverbs 3:12, whom does the LORD discipline?

Answer: The one He loves

Proverbs 3:12: "The LORD disciplines the one He loves, as does a father the son in whom he delights."

“My son, do not reject the discipline of the LORD, and do not loathe His rebuke; for the LORD disciplines the one He loves, as does a father the son in whom he delights.”— Proverbs 3:11-12 (BSB)