Surah Muhammad, ayah 24

أَفَلَا يَتَدَبَّرُونَ ٱلۡقُرۡءَانَ أَمۡ عَلَىٰ قُلُوبٍ أَقۡفَالُهَآ ٢٤

Afalā yatadabbarūnal-qur'āna am 'alā qulūbin aqfāluhā

Then do they not reflect upon the Qur’ān, or are there locks upon [their] hearts?