وَلَفْظُ السَّلَامِ دُونَ «عَلَيْكُمْ»
The specific Wajib wording in the concluding salutations is the word السَّلَامُ. The commentary explains the Salaam on the right and left; the additional wording عَلَيْكُمْ is not the part by which this particular Wajib is defined.
The complete Sunnah manner of the two Salaams is taught later.