Hilchos Lashon Hara, chapter 2, section 5

If someone spoke lashon hara before three people, one generally does not transgress the prohibition of lashon hara if one repeats it further. However, all this involves regular people. If the three were G-d fearing and careful to avoid lashon hara, or even only one of them, since it is not certain the story will be revealed, or in addition, if one of the three was the friend or relative of the person spoken of, one may not speak of it further, for his friend or relative will certainly not speak of it further in order to not bring their friend into disgrace.