Is it necessary to repeat the Dhuhr prayer after discovering the onset of menstruation following its completion, given that the menstrual cycle was delayed and its pains were present before the prayer?

If a woman is certain that the blood is menstrual blood, she must refrain from prayer and everything that requires purification. This blood she saw after Fajr (dawn) prayer is menstrual blood, because it appeared during a possible time and connected with what she was certain was menstruation. It is forbidden for a menstruating woman to pray during her period, based on the Prophet's (peace be upon him) saying to the menstruating woman: "...So when your menstruation begins, stop praying..." As for one who prayed while menstruating, thinking she was in a state of purity, there is no sin upon her, due to Allah's (the Almighty) saying: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended. And ever is Allah Forgiving and Merciful."