Is it permissible to spit lightly and seek refuge (with Allah) before prayer for one who suffers from obsessive doubts regarding the Takbir (Allahu Akbar) and the intention, and likewise for one who suffers from obsessive doubts regarding the pronunciation of Al-Fatiha or the surah after Al-Fatiha?

Spitting and seeking refuge (from Satan) are prescribed for anyone whose prayer has been confused by Satan, based on the Hadith of Uthman ibn Abi al-'As. The apparent meaning of Al-Nawawi's statement is that they are prescribed for anyone whom Satan whispers to, due to the Almighty's saying: "And if an evil suggestion comes to you from Satan, then seek refuge in Allah." (Quran 7:200) And whoever Satan whispers to during their prayer, let them seek refuge (with Allah) and spit to their left three times, then proceed with their recitation and remembrances, and that seeking refuge does not interrupt their recitation.