The believer defends the honor of others, and doesn't allow them to be slandered or their dignity besmirched.
In our latest Episode (Number 18), we discuss the concept of speaking up when others are slandered, and of not allowing false accusations or blatant lies to be left unchallenged. Even backbiting that occurs in a gathering, or evil insinuations based on assumptions, should not tacitly be allowed to slip by.
When Ka'b b. Mālik remained behind in the Battle of Tabuk, and the Prophet (SAW) asked about him, someone of the hypocrites slyly remarked that his wealth had distracted him and hence he wasn't in the expedition. But it was the scholar of the Companions, Mu'adh b. Jabal, who immediately retorted, "What an evil thing you have said! O Messenger of Allah, I have only seen good from him..."
The Prophet (SAW) said, "Whoever defends the honor of his brother shall have his face shielded from Jahannam on the Day of Judgment" [al-Adab al-Mufrad].