Which command does Paul call 'the first commandment with a promise' in Ephesians 6:2?

Answer: Honor your father and mother

Paul quotes "Honor your father and mother," whose promise is that it may go well with you and you may have a long life on the earth.

““Honor your father and mother” (which is the first commandment with a promise), “that it may go well with you and that you may have a long life on the earth.””— Ephesians 6:2-3 (BSB)