Answered by Ustadh Tabraze Azam
Question: I recently had a back operation. Some blood still flows from the operation. I noticed some blood from the operation flowing while I was praying. Am I allowed to pray with blood flowing as a result of an operation?
Answer: Wa alaikum assalam wa rahmatullahi wa barakatuh,
I pray that you are in the best of health and faith, insha’Allah.
If you are considered excused (ma`dhur), it would be permitted to pray whilst the excuse (bleeding in your case) is occurring.
In order to establish that you have an excuse, an entire prayer time must pass wherein you did not find enough time to perform a minimal ablution (wudu) and quick prayer, without the excuse occurring.
However, if you are able to pray sitting (on the floor) such that the excuse will not occur, then you must do so, and thus you will not be considered excused (ma`dhur).
See also: The Fiqh of Chronic Excuses and Ablution
And Allah alone gives success.