What is the ruling on the prayers of one who used to say "walaisa" (وليس) instead of "waladh" (ولاذ) in Al-Fatiha, and "al-adheem" (العضيم) instead of "al-atheem" (العظيم) in the bowing supplication, despite knowing of his doubt and his negligence in asking?

The person responsible for his condition has waswas (obsessive whispering/thoughts) concerning the articulation points of letters. If he recited Al-Fatihah to a Sheikh and no error was apparent from him, this confirms that he is afflicted with waswas, and he must turn away from these obsessive thoughts. If he unintentionally replaces the letter dhāl (ذ) with dāl (د) in Al-Fatihah, there is no sin upon him, and his prayer is valid according to the Maliki school, and he is permitted to follow this opinion. As for replacing the letter ẓāʾ (ظ) with ḍād (ض) in the word "Al-Aẓīm" (العظيم), it does not cause harm due to the proximity of the two letters in their articulation point.