One of four Hindu texts in five days (4)
I believe the answer is:
veda
'one of four hindu texts' is the definition.
'in five days' is the wordplay.
'in' indicates the answer is hidden within the clue.
'VEDA' is hidden within 'five days'.
(Other definitions for veda that I've seen before include "Hindu scriptures" , "Sacred text of Hinduism" , "Most sacred literature of Hinduism" , "holy book" , "Most ancient and sacred literature of Hindus" .)