وَقَالَ أَبُو يُوسُفَ: يَقْضِي أَرْبَعًا.
Translation: Abu Yusuf said that four rakahs must be made up.
Abu Yusuf regards the commitment arising from a single opening as covering all four rakahs, so invalidating the later pair leads to makeup of four.
The other Hanafi view treats the first properly completed pair as independent once its sitting is performed, leaving only the later pair to make up. The issue is the status of two pairs under one opening.
Opening interactive controls...
Voluntary Prayers: Regular Sunnahs, Nawafil and Juristic Differences
وَقَالَ أَبُو يُوسُفَ: يَقْضِي أَرْبَعًا.
Translation: Abu Yusuf said that four rakahs must be made up.
Abu Yusuf regards the commitment arising from a single opening as covering all four rakahs, so invalidating the later pair leads to makeup of four.
The other Hanafi view treats the first properly completed pair as independent once its sitting is performed, leaving only the later pair to make up. The issue is the status of two pairs under one opening.