Azad Sarv and the Book of Kings

From C9.1, The Prelude. It illustrates C9.1.3–7:

C9.1.3
There was an ancient man named Azad Sarv,Who lived with Ahmad, son of Sahl, in Marv.
C9.1.4
He held a book of kings from days of old;His frame was cast within a hero’s mold.
C9.1.5
His heart held eloquence, his mind held lore,His tongue preserved the tales of days before.
C9.1.6
His line from Sahm, Nariman’s son, was drawn;He knew how Rostam fought and then was gone.
C9.1.7
What I received from him I now rehearse,And weave it, word by word, into my verse.