In Islam He said in the Qur'an 112:1-4 (Chapter of Purity or TAWHID-the oneness of Allah.)
In the name of Allah Most Gracious, Most Merciful
1 Say: He is Allah, the One and Only;
2 Allah, the Eternal, Absolute;
3 He begetteth not, nor is He begotten;
4 And there is none like unto Him.
Islam is based on monotheism.
Tawhid, the oneness of Allah, is an essential belief for all Muslims.
The oneness of Allah is the one most important theological principal in Islam. The first of the five pillars, the declaration of faith, which is the first act that one does to embark on Islam, reiterates the necessity of the belief in the oneness of Allah. It begins with the negation of any god other than Allah:
"I bear witness that there is no god but Allah and that Mohammed is His messenger."
YouTube - ‪Description of Allah -SWT- (Video + Audio)‬‏