Allah says; 

وَإِلَـهُكُمْ إِلَهٌ وَاحِدٌ لاَّ إِلَهَ إِلاَّ هُوَ الرَّحْمَنُ الرَّحِيمُ
 
 

And your Ilah (God) is One Ilah (God ـ Allah), La ilaha illa Huwa (there is none who has the right to be worshipped but He), the Most Gracious, the Most Merciful.

In this Ayah, Allah mentions that He is the only deity, and that He has no partners or equals. He is Allah, the One and Only, the Sustainer, and there is no deity worthy of worship except Him. He is the Most Gracious ـ Ar-Rahman, the Most Merciful ـ Ar-Rahim.

We explained the meanings of these two Names in the beginning of Surah Al-Fatihah.

Shahr bin Hawshab reported that Asma' bint Yazid bin As-Sakan narrated that Allah's Messenger said:

 اسْمُ اللهِ الاَْعْظَمُ فِي هَاتَيْنِ الاايَتَيْنِ

Allah's Greatest Name is contained in these two Ayat:

وَإِلَـهُكُمْ إِلَهٌ وَاحِدٌ لاَّ إِلَهَ إِلاَّ هُوَ الرَّحْمَنُ الرَّحِيمُ


And your Ilah (God) is One Ilah (God ـ Allah), La ilaha illa Huwa (there is none who has the right to be worshipped but He), the Most Gracious, the Most Merciful.

and:

الم


اللّهُ لا إِلَـهَ إِلاَّ هُوَ الْحَيُّ الْقَيُّومُ
 
 
Alif-Lam-Mim. Allah! La ilaha illa Huwa (none has the right to be worshipped but He), Al-Haiyul-Qaiyum (the Ever Living, the One Who sustains and protects all that exists)." (3:1-2)

Then Allah mentions some of the proof that He is alone as the deity, that He is the One who created the heavens and the earth and all of the various creatures between them, all of which testify to His Oneness.

Allah said