How can one get rid of the obsessive whispers concerning purity and creed that lead to doubt in the existence of Allah and all other matters of religion, causing one to lose certainty and affecting one's understanding? And is ghusl (ritual bath) required after experiencing such thoughts? And is one who suffers from them considered among the disbelievers or hypocrites? And will one be rewarded for righteous acts of worship despite these thoughts?

All that you are experiencing are whispers (waswas) from Satan, and you are upon Islam and have not departed from it because of these whispers that you detest. These whispers do not harm you, nor do they affect your faith, nor do they necessitate ghusl (ritual bathing) for you. Rather, you should ignore them and pay no attention to them, and seek Allah's help to get rid of them. You will be rewarded for struggling against them and for your patience with them, for they are a trial for which you will be rewarded. You are not among the disbelievers or the hypocrites. Your acts of worship are valid both before and after these whispers, and you should not discontinue any of your acts of worship because of them. These whispers are not a punishment from Allah; rather, they may be for raising your rank, refining your faith, and increasing your steadfastness. Your question indicates goodness, love for the religion, and a strong desire for healing. With the sincerity of this desire, healing will occur, Allah willing.