Surah Al-Isra Verse 53

2238 This command refers to two situations. (1) Even to your enemies and the enemies of Allah you should speak fair: who are you to judge others? Judgment belongs to Allah alone, for He knows you (i.e., all mankind) best, and your personal knowledge is at best imperfect. And Satan is always trying to divide mankind. (2) Amongst yourselves, also you should not entertain suspicions, but speak politely according to the best standards of human speech. A false or unkind word may destroy all your efforts at building up unity, because the forces of disruption are more numerous than the forces of unity.