Quran 47:24 from Surah Muhammad on Divine Marvels.
أَفَلَا يَتَدَبَّرُونَ ٱلۡقُرۡءَانَ أَمۡ عَلَىٰ قُلُوبٍ أَقۡفَالُهَآ
English translation: Then do not they ponder (over) the Quran or upon (their) hearts (are) locks
Transliteration: afala yatadabbaruna al-qur'ana am ala qulubin aqfaluha