Doctrine and Covenants 91: Revelation given through Joseph Smith the Prophet, at Kirtland, Ohio, March 9, 1833. HC 1: 331-332. The Prophet was at this time engaged in the translation of the Old Testament. Having come to that portion of the ancient writings called the Apocrypha, he inquired of the Lord and received this instruction.
1-3, The Apocrypha is mostly translated correctly but contains many interpolations by the hands of men that are not true; 4-6, It benefits those enlightened by the Spirit.
[Source: Doctrine and Covenants, http://amzn.to/DoctrineandCovenants]