What is the meaning of not paying attention to the whispers (waswas) of ablution (wudu) and prayer (salat), and does this include continuing to perform acts of worship despite feeling that they are not accepted or are invalid, and overcoming whispers such as "I have not entered into prayer" simply by saying the opening takbir, as a way to gradually get rid of these whispers?

The most important cure for whisperings (waswas (definition)) is to ignore them and not pay attention to them. This means not acting upon the dictates of these whisperings. For example, after the opening takbeer (takbeerat al-ihram (definition)), do not repeat the takbeer, and believe that what you have done is correct. Similarly, if you perform the prayer while feeling that it is not accepted, or that it is invalid, or that it is merely movements, do not interrupt it because of these doubts. By consistently adhering to this method, you will rid yourself of the whisperings.