38:1
صٓ ۚ وَٱلْقُرْءَانِ ذِى ٱلذِّكْرِ
sad wal-qur'āni dhī l-dhik'ri
Sad By the Quran with its reminding . . .!
Sâd. [These letters (Sâd etc.) are one of the miracles of the Quran and none but Allah (Alone) knows their meanings]. By the Quran full of reminding.