Tafsir of Al-Waqi'ah 56:25

(They shall not hear therein any vain talk)

It is speech that is not worth considering, being that which is uttered without deliberation or thought. It runs the course of lagha (chatter), which is the sound of sparrows and similar birds. Sometimes, everything ugly is termed lagha.

(Nor any sinful speech)

That is, nor an attribution of sin; meaning, it will not be said to them, "You have sinned." Ibn Abbas—as recorded by Ibn al-Mundhir and Ibn Abi Hatim—interpreted it as "lying." Hannad also recorded it from al-Dahhak. This is from the metaphorical (majaz), as is not hidden, and the speech belongs to the category of, "And you will not see the lizard enter its hole."