Mujahid said concerning this verse: "Those are declared innocent of what they say": The reason is that whatever good word a disbeliever says belongs to the believer, and whatever wicked word a believer says belongs to the disbeliever; each is held free of speech that is not rightfully his.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19561