The Princes Break Sarv's Frost Spell

From A6.5, Sarv Tests Fereydoon’s Sons. It illustrates A6.5.5–10:

A6.5.5
But Sarv, the sorcerers’ king, devised his guile,And left the royal garden for a while.
A6.5.6
He worked his spell and raised a deadly cold,With roaring winds to kill those princes bold.
A6.5.7
The meadow froze; the plain lay iron-white,No crow could cross the air in such a night.
A6.5.8
The spell-breaking Shah’s three sons sprang from sleep,When bitter cold had pierced the garden deep.
A6.5.9
Divine farr guarded them, and wisdom’s power;Their royal knowledge braced them in that hour.
A6.5.10
With royal afsun, steadfast in the cold,They barred the spell and broke its deadly hold.