Ayat al-Kursi is verse 255 of the second chapter (Surah) of the Holy Quran, Surat al-Baqarah (The Chapter of the Cow)

اللَّهُ لاَ إِلَهَ إِلاَّ هُوَ الْحَيُّ الْقَيُّومُ لاَ تَأْخُذُهُ سِنَةٌ وَلاَ نَوْمٌ لَهُ مَا فِي السَّمَاوَاتِ وَمَا فِي الأَرْضِ مَنْ ذَا الَّذِي
يَشْفَعُ عِنْدَهُ إِلاَّ بِإِذْنِهِ يَعْلَمُ مَا بَيْنَ أَيْدِيهِمْ وَمَا خَلْفَهُمْ وَلاَ يُحِيطُونَ بِشَيْءٍ مِنْ عِلْمِهِ إِلاَّ بِمَا شَاءَ وَسِعَ كُرْسِيُّهُ السَّمَاو ;َاتِ وَالأَرْضَ وَلاَ يَئُودُهُ حِفْظُهُمَا وَهُوَ الْعَلِيُّ الْعَظِيم


Allahu la ilaha illa Huwa, Al-Haiyul-Qaiyum La ta'khudhuhu sinatun wa la nawm, lahu ma fis-samawati wa ma fil-'ard Man dhal-ladhi yashfa'u 'indahu illa bi-idhnihi Ya'lamu ma baina aidihim wa ma khalfahum, wa la yuhituna bi shai'im-min 'ilmihi illa bima sha'a Wasi'a kursiyuhus-samawati wal ard, wa la ya'uduhu hifdhuhuma Wa Huwal 'Aliyul-Adheem


"Allah! There is no god but He - the Living, The Self-subsisting, Eternal. No slumber can seize Him Nor Sleep. His are all things In the heavens and on earth. Who is there can intercede In His presence except As he permitteth? He knoweth What (appeareth to His creatures As) Before or After or Behind them. Nor shall they compass Aught of his knowledge Except as He willeth. His throne doth extend Over the heavens And on earth, and He feeleth No fatigue in guarding And preserving them, For He is the Most High. The Supreme (in glory)."
[Surah al-Baqarah 2: 255]