Question 91: When a person comes to the Masjid (mosque) before Athaan (call to Prayer), offers the obligatory Salaah (Prayer), sits to recite the Qur’aan and the Mu’addin (caller to Prayer) announces the Athaan while he is reciting; which is better to recite subvocally while the Mu’adhin is announcing the Athaan until he ends the fourth time of Takbeer (saying: “Allaahu Akbar” i.e. Allaah is the Greatest) of the first part of Athaan, then he stops reciting and follows the Mu’aththin from the beginning except when the Mu’aththin says: “Hayyi `Alaa Al-Salaah (Come to Salaah)” and “Hayyi `Alaa Al-Falaah (Come to success).” He would then follow the Mu’aththin until he completes Athaan to get the two rewards: the reward of following the Mu’aththin and that of the recitation done at the beginning of Athaan? Or should a person repeat after the Mu’aththin and stop recitation?
Answer: It is Sunnah (action following the teachings of the Prophet) to stop recitation and repeat after the Mu’aththin word by word. The Prophet (peace be upon him) said: “When you hear the Mu’addin, repeat what he says.” (Agreed upon by Bukhaaree and Muslim)... read more here.