إن آخر الوقت في الفجر كامل، وإنما يصير الوقت فاسداً بطلوع الشمس، وذلك بعد خروج الوقت
The final segment of Fajr is complete; sunrise brings the disapproved state after that prayer's time has ended.
A prayer in progress when the sun rises has a particular Hanafi ruling. This differs from Asr toward sunset because the disapproved period enters only after the appointed Fajr period has ended.
The key is to distinguish a defect occurring within the period from a new disapproved state beginning beyond the period. Merely saying “near the end of prayer time” conceals this difference.