67:13
وَأَسِرُّوا۟ قَوْلَكُمْ أَوِ ٱجْهَرُوا۟ بِهِۦٓ ۖ إِنَّهُۥ عَلِيمٌۢ بِذَاتِ ٱلصُّدُورِ ١٣
Saheeh International
And conceal your speech or publicize it; indeed, He is Knowing of that within the breasts.
Tafsir of "Ibn Kathir" (English)
And whether you keep your talk secret or disclose it, verily, He is the All-Knower of what is in the breasts.meaning, that which occurs in the hearts (ideas, thoughts, etc.)