Is the creed of the Turkish writer Harun Yahya sound, especially his statement: "Matter is but a glimpse; God cannot exist outside of this diverse matter; God is everywhere; nothing can exist outside of God's existence"?

The statement mentioned is not based on a sound creed; rather, its outward appearance suggests the belief in Hulool (incarnation) and Ittihad (union with God), and this belief is indeed kufr (disbelief), even among the gravest forms of kufr.