Do the Fajr, Dhuhr, and Asr prayers become invalid if traces of mathy (pre-seminal fluid) are discovered on the underwear after performing them and before changing for Maghrib?

Al-madhy is a viscous fluid that exits upon arousal of desire. It is impure and invalidates ablution. To purify oneself from it, it suffices to wash the private parts and sprinkle water on the garment. The questioner's prayer is valid, and he is not required to repeat it for two reasons: First, he is not certain about the time the madhy exited, and doubt after completing an act of worship is not to be heeded. Second, whoever prayed with impurity, being ignorant of its presence, or knowing it then forgetting it, his prayer is valid according to the most preponderant opinion; because Allah does not burden a soul beyond its capacity, and He has lifted accountability from the ignorant and the forgetful. The specific proof for this is that the Prophet, peace and blessings be upon him, did not restart his prayer when Jibril informed him of the presence of filth on his sandals.