Hilchos Lashon Hara chapter 10, section 15

We see that when relying on this leniency a person is in great danger of speaking lashon hara if he does not observe all the details involved, especially nos. 2 and 4. Regarding this, Life and death are in the hand of the tongue (Proverbs 18:21). If a person does not think carefully before speaking he will certainly stumble, because as he talks he becomes overcome with anger and a person cannot guard against this. Therefore, one must plan what to say before speaking.