This is a third instance of discipline directed at those who hear evil talk, believe it to some extent, and start to spread it; they should not spread such talk or pass it on to others. Allah says:
(Verily, those who like that Fahshah should be circulated among those who believe, they will have a painful torment) meaning, those who like to see evil talk about them (the believers) appear,
(they will have a painful torment in this world) means, because of the prescribed punishment, and in the Hereafter because of the torment in Hell.
(And Allah knows and you know not.) means, return the matter to Him and you will be guided. Imam Ahmad recorded from Thawban that the Prophet said:
(Do not annoy the servants of Allah, nor abuse them, nor seek their hidden shortcomings. Whoever seeks out the faults of his Muslim brother, Allah will expose his faults and degrade him, even if he is hiding in his house.)