Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
258. Chapter: On the prohibition against carrying tales and things that people have said to those in authority if there is no need for that, for instance, fear of corruption, etc.
Allah Almighty says, "Do not help one another to wrongdoing and enmity." (5:2)
1539. Ibn Mas'ud reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "None of my Companions should convey to me anything bad about someone else. I want to come out to you with a clear heart." [Abu Dawud and at-Tirmidhi]