Blake originally used this image as the frontispiece of Europe a Prophecy. However he reused the copper plate to make additional prints which are known by the title 'Ancient of Days'. Two passages which appear to be sources for the image are from the Bible and from Paradise Lost.
Europe a Prophecy
New York Public Library
S. Foster Damon, in A Blake Dictionary gives this description of the process of creation as Blake understood it:
"Creation is not the beginning of existence, for all things are eternal: it is a consequence of the fall toward 'Eternal Death' (separation from Eternity)...
The process of Creation is one of dividing up the original Unity. Beginning with the separation of light from darkness, it proceeds through the six Days of Creation, culminating in the separation of man from God. After that the sexes are divided in the creation of Eve; Good and Evil, in the eating of the fruit; man and happiness in the expulsion from the Garden; soul and body, in the first murder; man from his brother in the confusion of tongues at Babel." (Page 94)
This print in the Whitworth Gallery, University of Manchester, is thought to be the last print of this image made by Blake
 The LORD possessed me [Wisdom] in the beginning of his way, before his works of old.
 I was set up from everlasting, from the beginning, or ever the earth was.
 When there were no depths, I was brought forth; when there were no fountains abounding with water.
 Before the mountains were settled, before the hills was I brought forth:
 While as yet he had not made the earth, nor the fields, nor the highest part of the dust of the world.
 When he prepared the heavens, I was there: when he set a compass upon the face of the depth:
John Milton, Paradise Lost, Book 7
"and in his hand
He took the golden Compasses, prepar'd
In Gods Eternal store, to circumscribe
This Universe, and all created things:
One foot he center'd, and the other turn'd
Round through the vast profunditie obscure,
And said, thus farr extend, thus farr thy bounds,
This be thy just Circumference, O World.
Thus God the Heav'n created, thus the Earth,"
Auguries of Innocence, (E 495)
"Which was Born in a Night to perish in a Night When the Soul Slept in Beams of Light God Appears & God is Light To those poor Souls who dwell in Night But does a Human Form Display To those who Dwell in Realms of day"