Surah Al-Mulk 67:13

وَأَسِرُّوا۟ قَوْلَكُمْ أَوِ ٱجْهَرُوا۟ بِهِۦٓ ۖ إِنَّهُۥ عَلِيمٌۢ بِذَاتِ ٱلصُّدُورِ

And conceal your speech or publicize it; indeed, He is Knowing of that within the breasts.

Translation: Saheeh International

Tafsir

And whether you keep secret O people your speech or proclaim it He indeed exalted be He is Knower of what is in the breasts of what they contain so how much more so is He Knower in the case of what you utter openly — the reason for the revelation of this verse was that the idolaters said to one another ‘Speak secretly …

Excerpt from Tafsir al-Jalalayn, commentary on 67:13, via Quran.com. The reader has the full commentary and 9 more tafsirs.