Islam:
Say: Allah(GOD) is one,the Eternal GOD. He begot none,nor was He begotten. None is equal to Him.
Ref: Quran (112)

Christianity & Judaism:
Hear, O Isreal, The Lord, Our GOD, is one Lord.
Ref: The Bible,Mark (12:29); Deuteronomy (6:4)

Hinduism:
He is One without a second.
Ref: Chandogya upanishad (6:2:1)

Sikhism:
There exists but One GOD. Who is called THE True, The Creator.
Ref: Siri Gurru Granth Sahib, (Vol:1, Japji verse:1)

Zoroastrians (Parsis):
He is One, He is without an origin or end. He has no father or mother, wife or son.
Ref: Dasatir, Ahura Mazda