وَقَدْ يُحْذَفُ الْفَاعِلُ، وَيُقَامُ الْمَفْعُولُ مَقَامَهُ إِذَا كَانَ الْفِعْلُ مَجْهُولًا، نَحْوُ: «ضُرِبَ زَيْدٌ»، وَهُوَ الْقِسْمُ الثَّانِي مِنَ الْمَرْفُوعَاتِ.
Translation: The subject may be omitted and the object given its position when the verb is passive, as in “ضُرِبَ زَيْدٌ.” This introduces the second class of nominatives.
The promoted element is called nāʾib al-fāʿil, the passive subject. Its full chapter comes next; here we establish the basic contrast.