What is the ruling on blood that is discharged due to forgetting contraceptive pills or being late in taking them: is it considered menstruation or istihadah (non-menstrual vaginal bleeding), and is it obligatory to change the sanitary pad for every prayer if it is considered istihadah?

If menstruation is disrupted due to birth control pills, and you do not have a regular cycle, then rely on distinguishing between menstrual blood and abnormal vaginal bleeding (istihada). Menstrual blood is black or dark, has a foul odor, is often accompanied by pain, and does not clot after exiting the body. If the blood has these characteristics, it is menstruation, and you should refrain from praying and fasting during it. However, if the blood has other characteristics, it is istihada. If the total number of bleeding days exceeds 15 days, then anything beyond that is considered istihada. As for the woman experiencing istihada, she must take precautions to prevent the spread of blood, perform ablution for each prayer, and is not required to change her sanitary pad for every prayer unless she was negligent in placing and securing it.