Quran 50:18 from Surah Qaaf on Divine Marvels.
مَّا يَلۡفِظُ مِن قَوۡلٍ إِلَّا لَدَيۡهِ رَقِيبٌ عَتِيدٞ
English translation: Not he utters any word but with him (is) an observer ready
Transliteration: ma yalfizu min qawlin illa ladayhi raqibun atidun