Is it permissible to say "La ilaha illa Allah" (There is no god but Allah), "Al-hamdu lillah" (Praise be to Allah), and engage in other forms of ذكر الله (remembrance of Allah) while listening to the Qur'an or in gatherings of ذكر (remembrance)?

It is recommended for someone who hears the Quran recited by someone other than their Imam in prayer to listen attentively. It is preferable for the listener not to be preoccupied with anything other than listening to the Quran. There is no harm if they say "La ilaha illa Allah" (There is no god but Allah), or "Alhamdulillah" (Praise be to Allah), or make remembrance of Allah, or supplicate, or seek refuge, especially if this occurs when hearing something that prompts remembrance or supplication. The remembrance of Allah in gatherings is a virtue, and its abandonment is a cause for regret. Interacting with dhikr (remembrance of Allah) and Quran recitation, and seeking humility and being affected by them, is praiseworthy in Islamic law if it is overwhelming and without pretense or artificiality.