A farewell at some stage repeated (2-2)
I believe the answer is:
ta-ta
'a farewell' is the definition.
(I've seen this before)
'at some stage repeated' is the wordplay.
'some stage' indicates an anagram (I've seen 'staged' mean this ('staged' can mean 'organised')).
'repeated' says to double the letters.
'at' with letters rearranged gives 'ta'.
'ta' duplicated is 'TA-TA'.
(Other definitions for ta-ta that I've seen before include "Bye!" , "Bye-bye" , "A Farewell" , "Cheerio" , "Adieu" .)