Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states that: Whether one is praying alone or in congregation, the proper rule to follow is to read silently in prayers known as silent prayers (as-sirriyyah) and to recite aloud in prayers that are termed as loud (al-jahriyyah). The silent prayers are Zhuhr and `Asr. The aloud prayers are Maghrib, `Isha’ and Fajr, as well as Tarawih, Tahajjud, Witr, Jumu`ah and `Eid prayers. It should be remembered that the last two prayers can only be prayed in congregation.

So if you are praying Zhuhr and `Asr alone, you should pray silently; but if you are praying Maghrib, `Isha’ and Fajr, you should read them loudly only to the extent that you can hear yourself [i.e., in a very low voice]. Likewise, you can recite aloud Witr and Tahajjud.”