The most common and most likely answer to this crossword clue is the 3 plus 8 plus 3 plus 3 plus 6 letter word THE THOUSAND AND ONE NIGHTS
I've seen this crossword clue in The Times
T
H
E
T
H
O
U
S
A
N
D
A
N
D
O
N
E
N
I
G
H
T
S
Buddy explains!
The straight part
We know that "Arabian saga" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case arabian saga = the thousand and one nights.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.