Sources Boehme 5

The 'Fall' in terms of Urizen's controversy with

Ahania, is found in Night Three of the Four Zoas;

"His visage changd to darkness & his strong right hand came forth 

To cast Ahania to the Earth he siezd her by the hair

And threw her from the steps of ice that froze around 

his throne

Saying Art thou also become like Vala. thus I cast thee out      

Shall the feminine indolent bliss. the indulgent self of

weariness
The passive idle sleep the enormous night & darkness of Death
Set herself up to give her laws to the active masculine virtue
Thou little diminutive portion that darst be a counterpart
Thy passivity thy laws of obedience & insincerity
Are my abhorrence. Wherefore hast thou taken that fair form
Whence is this power given to thee! once thou wast in my breast
A sluggish current of dim waters. on whose verdant margin
A cavern shaggd with horrid shades. dark cool & deadly. where
I laid my head in the hot noon after the broken clods
Had wearied me. there I laid my plow & there my horses fed
And thou hast risen with thy moist locks into a watry image
Reflecting all my indolence my weakness & my death
To weigh me down beneath the grave into non Entity
Where Luvah strives scorned by Vala age after age wandering 
Shrinking & shrinking from her Lord & calling him the Tempter
And art thou also become like Vala thus I cast thee out.
So loud in thunders spoke the King folded in dark despair
And threw Ahania from his bosom obdurate She fell like lightning
Then fled the sons of Urizen from his thunderous throne petrific
They fled to East & West & left the North & South of Heaven
A crash ran thro the immense The bounds of Destiny were broken
The bounds of Destiny crashd direful & the swelling Sea
Burst from its bonds in whirlpools fierce roaring with Human
voice
Triumphing even to the Stars at bright Ahanias fall
Down from the dismal North the Prince in thunders & thick clouds

As when the thunderbolt down falleth on the appointed place
Fell down down rushing ruining thundering shuddering
Into the Caverns of the Grave & places of Human Seed
Where the impressions of Despair & Hope enroot forever
A world of Darkness. Ahania fell far into Non Entity

(Erdman 328-330)

Blake acted on scriptural grounds for this story, ie the Flood.  We are told

that God's wrath was invoked because the Nephilim found the daughters

of men fair and violence filled the land.

In Percival 180-83 continues to discuss the Fall:
"In Paradise, says Boehme, Adam lived in an inward principle, and so
living he had control  over the four elements, but when he moved outward
into the "external humanity", the four elements got control of him."

At the bottom lies Urizen 'in a stonied stupor', helpless before the
hugh inpouring of sense impressions... in the fact of casting out Ahania,
Urizen's visage changed to darkness...he became a blind and impotent
figure.

Adam became corrupt and weary, and fell into a sleep.  Here he was
undone and if the mercy of God had not help and made a women out
of him, he would still be asleep.....the earlier monism was replaced by
duality.

There are many sources outside Scripture; the void or abyss into which

the Zoas fall is of the same nature as the abyss in  Boehme, where it's

the world of God the Father in separation from the Son, the dark

fire-source in separation from the light, the first principle alone, without

manifestation; it's the world into which Lucifer and his cohorts fall.

(Boehme, Threefold Life, viz Mysterium magnum)

Notice how this compares with Blake's drawing on Plate 36 of The Book of Milton: