Answered by Ustadh Tabraze Azam
Question: If one is reasonable sure that when one begins to bleed at the time of fajr, does one need to wait till the end of dhur to establish if one has a chronic excuse or not? Or can one pray dhur at any point of dhur time without waiting till the end if one is unable to pray at the end in the case if one is at work?
Answer: Wa alaikum assalam wa rahmatullahi wa barakatuh,
I hope you are in the best of health and spirits, insha’Allah.
No, you would need to wait and pray towards the end of the time. [Ibn `Abidin, Radd al-Muhtar]
If you can pray sitting (for example) such that the bleeding does not occur, then you must do so. As long as the bleeding is stopped (by such sitting), you would not need to wait until the end of the prayer time to pray.
The excuse is only established after an entire prayer time has passed such that one did not find enough time to perform a quick ablution and prayer. Without this, you will not be considered an excused person, and would be required to wait. [ibid.]
See also: The Fiqh of Chronic Excuses and Ablution
And Allah alone gives success.
Checked & Approved by Faraz Rabbani