Salutation upset mother, sad to say (6)
I believe the answer is:
salaam
'salutation' is the definition.
(thesaurus)
'upset mother sad to say' is the wordplay.
'upset' says the letters should be written backwards.
'mother' becomes 'ma' (ma is a kind of mother).
'sad to say' becomes 'alas' (I've seen this before).
'ma'+'alas'='maalas'
'maalas' backwards is 'SALAAM'.
(Other definitions for salaam that I've seen before include "Eastern greeting" , "Oriental salutation meaning peace" , "Muslim form of salutation" , "Muslim greeting signifying peace" , "An Oriental greeting meaning peace" .)