For sacred works put on holy robes in sober company (6)
I believe the answer is:
avesta
'for sacred works' is the definition.
(sacred texts in Zoroastrianism)
'put on holy robes in sober company' is the wordplay.
'put on holy robes' becomes 'vest' (put on vestments).
'in' is an insertion indicator.
'sober company' becomes 'AA' (Alcoholics Anonymous).
'vest' placed within 'aa' is 'AVESTA'.
(Other definitions for avesta that I've seen before include "holy text" , "Zoroastrian sacred writings" , "Zoroastrian scriptures" , "collection of sacred writings" , "Parsee scriptures" .)