The Ruling on Omitting the Audible or Quiet Recitation in Prayer

Question:
Honorable Shaykh, if one recites quietly in a prayer where the recitation is supposed to be audible, is the prostration for forgetfulness sufficient? And if it was done intentionally, does it invalidate the prayer?

Answer:
It does not invalidate it, because the audible recitation is a recommended practice (sunnah). So if one prays at night quietly and does not recite audibly, his prayer is valid, but he has missed the recommended practice. Yes. And if he recites audibly during the day and omits the quiet recitation, his prayer is valid, but he has left the recommended practice, which is the quiet recitation. If one omits the audible or quiet recitation out of forgetfulness, it is recommended for him to perform the prostration for forgetfulness, because whoever omits a recommended practice of the prayer out of forgetfulness, it is recommended for him to perform the prostration for forgetfulness. As for the prostration for forgetfulness due to omitting an obligatory act, or due to an addition or subtraction in the prayer, it is obligatory. But for omitting a recommended practice, it is recommended. Yes.