Surah Al-Mulk, ayah 13

67:13

وَأَسِرُّواْ قَوۡلَكُمۡ أَوِ ٱجۡهَرُواْ بِهِۦٓۖ إِنَّهُۥ عَلِيمُۢ بِذَاتِ ٱلصُّدُورِ ١٣

Wa asirrū qawlakum awijharū bihī innahū 'alīmu bidhātis-sudūr

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