The Witness, The All-Observant, The Testifier.

Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Ash-Shaheed (in Arabic: ٱلْشَّهِيدُ) meaning the one who is omnipresent and all-observing. There is nothing that we do that goes unnoticed, as He is ever-present and sees everything. His knowledge comprehends all, and He will be the ultimate witness on the day of judgment.