What is incumbent upon one who is afflicted with an annoying itch and excessive saliva during Wudu and prayer, causing him discomfort and delay? And what is the appropriate guidance for him?

If a person is afflicted with waswas (whispers/obsessive thoughts), they should disregard them and pay them no mind. Itching during prayer does not invalidate it if it is necessary, even if frequent; jurists have made an exception for this from the category of excessive actions that invalidate prayer, if the person cannot bear to refrain from it. As for itching during ablution (wudu'), it does not invalidate it. Regarding saliva, one must swallow it, and that does not cause harm. By disregarding these waswas, they will disappear, by the will of Allah.