On January 3, 1946, Wisliceny admitted in court that Jews sent to Auschwitz from Hungary were "brought to the final solution". On February 19, 1944, a document on executions in Piaski gave a list of Jews who were "brought to the final solution." ["der Endlösung zugeführt wurden" [YVA O.53/82, pp.50-52]. These types of executions had been defined by Heydrich as special treatment [Sonderbehandlung], as quoted here. We therefore have a convergence of documentation and testimony that "final solution" in the context of SS operations in Auschwitz and in Poland generally meant killing, albeit disguised as "special treatment" [Sonderbehandlung] in which death was meted out via extralegal executions.
The full document is in VEJ 9, Dok. 285, pp.784-787. A scan of the document is below.