When sending prayers upon Prophet Muhammad (peace be upon him) Imam Qazwini praises him (saw) as below:

و أفضل من أوتي الحكمة و فصل الخطاب 

“…the most virtuous of those who were given wisdom and the clear (or clarifying/distinguishing) address”

“فصل الخطاب” is an example of a sifah made mudaaf to its mawsoof. We saw examples of such cases very briefly in a previous post

Imam Taftazani explains that it could mean “الخطاب المفصول” or “الخطاب الفاصل”. 

فصل is a masdar and masdars are not directly attributed to entities e.g. as sifah (adjective) in mawsoof-sifah or khabr (predicate) in mubtada-khabr (subject-predicate). So when it exists in a mudaf/mudaf-ilayh structure that masdar can be in the meaning of either its Ismul Fa’il or Ismul Maf’ool. In this case it’s الفاصل (Ismul Fa’il) or المفصول (Ismul Maf’ool).

الخطاب المفصول would mean “separated speech” i.e. every portion of it is distinct and clear.

الخطاب الفاص would mean “the distinguishing address” i.e. the address that distinguishes between truth and falsehood.