What is the way to definitively get rid of obsessive-compulsive whispers (waswasah) in prayer and purity that lead to repeating actions again and again?

The treatment for obsessive thoughts is to turn away from them and ignore them. If Satan instills the obsessive thought to repeat an act of ablution (wudu) or prayer (salat), one should not give in to the obsession or succumb to Satan's doubts. With the help of Allah, these obsessive thoughts will disappear. You can also consult the "Consultations" section of the website or trusted doctors.