Is it permissible for me to follow the Maliki school of thought regarding the purity of a dog's saliva, even though there are proofs of its impurity, such as Ibn Umar's deduction that dogs used to spend the night in the mosque in the beginning [of Islam], and the Prophet's command to purify mosques?

If you suffer from obsessive-compulsive disorder (OCD), there is no benefit in researching the sayings of scholars; in fact, it may only increase your confusion. It is permissible for you to adopt the Maliki school of thought on this matter out of necessity, as some scholars have held the permissibility of seeking concessions, for "disagreement is a mercy, as concessions are a mercy."

Strive to disregard these intrusive thoughts and pay no attention to them, for that helps in getting rid of them. The one afflicted by intrusive thoughts must ignore them, otherwise, they would be an embodiment of the statement by Imam al-Haramayn: "Obsessive thoughts originate from ignorance of the paths of Sharia, or a deficiency in the instinct of intellect."

In addition to that, commit to dhikr (remembrance of God), reciting the Quran, and ruqyah shar'iyyah (Islamic exorcism/healing).