Recite Aloud or Quietly?
Question:
If a person misses a Rak'ah from the Fajr prayer should he complete it reciting audibly, or quietly?
Answer:
He may choose to do either, but it is better to complete it quietly, because there might be someone else completing his prayer and it would disturb him if he recited aloud.
Shaykh Muhammad bin Saalih al-`Uthaymeen
Fataawa Arkanaul-Islaam p.476 DARUSSALAM
