In this week's Parsha, we see Yosef telling Lashon Hora about his brothers. What Yosef reported were actions that he thought were sins on their part; however, in actuality, their actions were misinterpreted based on the way Yosef saw his brothers behave.
Some examples of this may be found in a passage in the Talmud Yerushalmi in Peiah (פרק א' הלכה א', דף ד.) which states that Yosef told Yaakov that he saw the brothers consume flesh torn from a living animal that had not been slaughtered, which was a forbidden act. Truthfully, however, the brothers did no such act; Yosef simply misinterpreted what he saw. Yosef might have seen the brothers eating from meat that still quivered after being slaughtered, which is permissible, or he may have seen the brothers eating an animal fetus from a mother that had been slaughtered which is also permissible. This fetus doesn't have to be slaughtered and what the brothers did was therefore allowed. Hashem punished Yosef מדה כנגד מדה, measure for measure, for his Lashon Hora, saying that for speaking Lashon Hora about his brothers when they really did nothing wrong, because they ate meat which indeed had been previously slaughtered, they will show Yosef's coat dipped in the blood of a goat that had been previously slaughtered to their father.
Another example of Yosef's Lashon Hora is when he tells his father that he heard his brothers call Bilhah's and Zilpah's sons slaves. This was also a misinterpreted accusation by Yosef. In actuality, the brothers called the sons of Bilhah and Zilpah "sons of maids," referring to their mothers' original status before they married Yaakov. The brothers did not mean to imply that Bilhah and Zilpah or their sons were still slaves. They knew that Bilhah and Zilpah had lost their "slave" status when they had married Yaakov. Hashem then punished Yosef, saying that since he suspected the brothers wrongly concerning slavery, he himself will be sold as a slave.
A third example of Yosef's Lashon Hora was his saying that he saw his brothers dealing with Canaanite women. This was a true statement, but the brothers considered their transactions to be permissible, although Yosef did not. Hashem thus told Yosef that if he thinks he is so righteous, he will be tested via Potiphar's wife to see how he reacts to other women.
Although all of Yosef's reports were intended for the ultimate benefit of his brothers, he made the mistake of not investigating any of the matters thoroughly enough and thus accused his brothers of these terrible acts. Even if the brothers had indeed committed the sins of which Yosef accused them, he still acted in the wrong manner. Yosef should have first rebuked his brothers directly before telling his father of their crimes. Therefore, anything Yosef said was Lashon Hora, and Hashem thus punished Yosef for his words. We can learn from this that if one speaks Lashon Hora, whether his words are true or not, Hashem will punish him and we should thus refrain from speaking this way.