Nahj al-Balāgha

Hadith 2250
backbiting-slander
٤٦١. وَقَالَ (عليه ‏السلام): الْغِيبَةُ جُهْدُ الْعَاجزِ.
461. Amīr al-mu’minīn, peace be upon him, said: Backbiting is the tool of the helpless.
Source: al-Sharīf al-Raḍī