Source: Fatāwā Muḥammadīyah, Vol. 1, p. 366
Question:
If someone sneezes during prayer, is it permissible for him to say al-ḥamdu lillāh?
Answer:
Al-ḥamdu lillāh, waṣ-ṣalātu wa-s-salāmu ʿalā Rasūlillāh, ammā baʿd:
✔ If a person sneezes during prayer, it is not only permissible but in fact recommended for him to say al-ḥamdu lillāh, as there is a clear ḥadīth regarding this in Jāmiʿ al-Tirmidhī, Kitāb al-Ṣalāh.
✘ However, if another worshipper responds to the sneezer by saying yarḥamuka Allāh, that is not correct, because such speech is not appropriate within the prayer.
هٰذا ما عندي، والله أعلم بالصواب
