The Essence
Al-Waahid is the One, the Unique. There is none like Him in His essence, attributes, or actions. He is indivisible, has no partners, no parents, and no offspring.
In the Quran
وَإِلَهُكُمْ إِلَهٌ وَاحِدٌ ۖ لَا إِلَهَ إِلَّا هُوَ الرَّحْمَنُ الرَّحِيمُ
"And your god is one God (Waahid). There is no deity [worthy of worship] except Him, the Entirely Merciful, the Especially Merciful. (Surah Al-Baqarah 2:163)"
In Your Duas
قُلْ هُوَ اللَّهُ أَحَدٌ
"Say, 'He is Allah, [who is] One.'"
— Quran, Surah Al-Ikhlas 112:1