Should one abandon prayer and fasting when a brownish or reddish discharge appears intermittently three or four days before the menstrual period?

What a woman sees of brownish discharge and spotting before her menstrual period is not considered menses unless it is connected to blood or occurs within the usual duration of her period. If she sees red blood, it is considered menses if it appears at a time suitable for menstruation, because the default assumption for blood is that it is menstrual blood.