Surah At-Tur 52:12

ٱلَّذِينَ هُمْ فِى خَوْضٍ يَلْعَبُونَ

Who are in [empty] discourse amusing themselves.

Translation: Saheeh International

Tafsir

those who play around in vain talk in falsehood that is to say those who are busily engaged with their disbelief;

Excerpt from Tafsir al-Jalalayn, commentary on 52:12, via Quran.com. The reader has the full commentary and 9 more tafsirs.