How can prayer be valid when the Qur'an is intentionally distorted—such as by opening the letter "dal" in "na'budu" or the letter "nun" in "nasta'in," or the letter "sad" in "sirat"—given that Al-Nawawi mentioned in "Al-Majmu'" that prayer is not invalidated by such an act, despite the prohibition of intentionally doing so, knowing that whoever intentionally distorts the Qur'an may commit an act of disbelief (kufr)?

Lahn (grammatical or pronunciation error) in the Quran is not considered disbelief (kufr) unless it is done mockingly, stubbornly, by deeming lahn permissible, or by believing in its altered meaning. As for mere lahn, it is not associated with kufr according to the Shafi'is and others. Some scholars have gone further, stating that intentionally committing lahn that alters the meaning, while believing it to be correct or permissible, leads to kufr; because it is considered an introduction of something not part of the Quran, or because it is addressing Allah with human speech. However, they differed on whether prayer is invalidated by lahn that does not alter the meaning, and this is based on their difference of opinion regarding whether the miraculousness (i'jaz) lies solely in the composition (nazm), or in both the composition and grammar (i'rab) together.