فَخَبَرُ «إِنَّ» هُوَ الْمُسْنَدُ بَعْدَ دُخُولِهَا، نَحْوُ: «إِنَّ زَيْدًا قَائِمٌ».
Translation: The khabar of inna is the predicated information after this particle enters, as in “Indeed, Zayd is standing.”
Musnad is the information attributed to someone or something. Standing is predicated of Zayd, so «قَائِمٌ» is the khabar, not «زَيْدًا».