When Adhaan starts as one is Engaged in Reciting the Qur'aan

Q: Salaah-318: If the Adhaan starts while I am busy reciting the Qur'aan should I continue reciting or stop to reply to the Adhaan?

Answer: If you are in the Masjid, you may continue reciting, but if you are at home, stop to reply to the Adhaan. However, if the Adhaan is from a Masjid outside your locality, there is no harm in continuing recitation even if you are at home. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2