What is the ruling on articulating letters during prayer when there are bubbles in the mouth, and when there is no distinction between the emphatic ضاد (ḍād) and ظاء (ẓāʾ), along with difficulty in pronouncing the word "الضالين" (aḍ-ḍāllīn) correctly? And is it permissible to raise one's voice at the point of the letter if the pronunciation is faint during the rest of the prayer?

Whispering/obsessive doubts (waswasah) regarding the articulation points of letters (makharij al-huruf) is one of the most dangerous ailments, and scholars have warned against it. Exaggerated pronunciation, affected speech, and obsessive doubts in articulating letters are not part of the Sunnah of the Messenger of Allah, peace be upon him. Rather, they distract the person suffering from waswasah from understanding the recitation and cause them to miss out on humility (khushu') in prayer.

If you are suffering from waswasah, it is permissible for you to adopt the view of the Maliki school and Ibn Taymiyyah, which does not stipulate that the reciter must hear themselves. Rather, sufficiency is achieved by articulating the letters from their correct points of articulation and moving the tongue and lips, even if one does not hear oneself.

As for raising one's voice in a silent prayer with the aim of verifying pronunciation, this is a form of waswasah. Prayer is not invalidated by it, nor is a prostration of forgetfulness (sujud as-sahw) required for it.