Found it: http://wol.jw.org/en/wol/d/r1/lp-e/2004846
Watchtower 15th November 2004
When a Witness Is Wise
“A faithful witness is one that will not lie,” continues Solomon, “but a false witness launches forth mere lies.” (Proverbs 14:5) The lies of a false witness certainly can do much harm. Naboth the Jezreelite was stoned to death because two good-for-nothing men falsely testified against him. (1 Kings 21:7-13) And did not false witnesses come forward against Jesus, leading to his death? (Matthew 26:59-61) False witnesses also testified against Stephen—the first disciple of Jesus to be killed because of his faith.—Acts 6:10, 11.
A man of untruth may go unexposed for the time being, but consider his future. Jehovah hates “a false witness that launches forth lies,” states the Bible. (Proverbs 6:16-19) Such a man’s portion will be in the lake that burns with fire and sulfur—the second death—along with such wrongdoers as murderers, fornicators, and idolaters.—Revelation 21:8.
The faithful witness does not commit perjury when testifying. His testimony is not tainted with lies. However, this does not mean that he is under obligation to give full information to those who may want to bring harm to Jehovah’s people in some way. The patriarchs Abraham and Isaac withheld facts from some who did not worship Jehovah. (Genesis 12:10-19; 20:1-18; 26:1-10) Rahab of Jericho misdirected the king’s men. (Joshua 2:1-7) Jesus Christ himself refrained from divulging total information when doing so would have caused needless harm. (John 7:1-10) He said: “Do not give what is holy to dogs, neither throw your pearls before swine.” Why not? So that “they may never . . . turn around and rip you open.”—Matthew 7:6.