Hanafi
The sources give no view for it here.
أسباب انقلاب الحربي ذميًّا
بأي أسباب يصبح الحربي ذميًّا؟
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
انْقِلاَبُ الْحَرْبِيِّ ذِمِّيًّا: ٧ - يُصْبِحُ الْحَرْبِيُّ ذِمِّيًّا إِمَّا بِالتَّرَاضِي، أَوْ بِالإِْقَامَةِ لِمُدَّةِ سَنَةٍ فِي دَارِ الإِْسْلاَمِ، أَوْ بِالزَّوَاجِ، أَوْ بِالْغَلَبَةِ وَالْفَتْحِ، عَلَى خِلاَفٍ وَتَفْصِيلٍ يَأْتِي بَيَانُهُ فِي مُصْطَلَحِ (أَهْل الذِّمَّةِ) .
«الموسوعة الفقهية الكويتية» (Kuwait) entry «أهل الحرب» vol. 7 p. 106
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.