Hanafi
The sources give no view for it here.
ظهار العبد
هل يصح الظهار من العبد؟
Each school’s answer
In our wordsHanafi
Not stated in the sources
Maliki
Not stated in the sources
Shafi'i
Not stated in the sources
Hanbali
Not stated in the sources
The texts
مسألة: الظهار يصح من العبد، خلافا لمن منعه؛ لقوله تعالى: " الذين يظهرون منكم من نسائهم " فعم، ولأنه نكاح صحيح فصح فيه الظهار كنكاح الحر.
«الإشراف», al-Qadi Abd al-Wahhab p. 767
From the schools’ own books
Maliki
The sources give no view for it here.
Shafi'i
The sources give no view for it here.
Hanbali
The sources give no view for it here.
What is «in our words» is our standard wording; the books’ texts stay as they are.