Zaid Alsalami, Shaykh Dr Zaid Alsalami is an Iraqi born scholar, raised in Australia. He obtained a BA from Al-Mustafa University, Qom, and an MA from the Islamic College in London. He also obtained a PhD from... Answered 3 months ago

Bismihi ta'ala

If one had enough time, and intentionally did not perform ghusl before Fajr time, then their fasting for that day will be invalid, and they must redo that day as qadha` and pay kaffarah

If they did not have enough time, or it was not intentional for them to stay in janabah, then their fasting is valid.

And Allah knows best.