I would like to perform a two-Rak‘ah voluntary prayer; should it be performed out loud or in a low tone?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

With regards to voluntary prayers, the Sunnah of the Prophet, sallallaahu ‘alayhi wa sallam, is that voluntary prayers are performed in a low tone during the day and out loud at night.

Mujaahid said, "Prayers in the daytime are in a low tone." Hence, worshippers should not perform prayers out loud during the daytime except for the Jumu‘ah prayer and the two ‘Eid prayers.

Therefore, if you perform this two- Rak‘ah voluntary prayer during the daytime, the Sunnah is to perform it in a low tone. If you perform it at night, you should perform it out loud.

Allaah Knows best.