There is no need to recite aloud when You are praying alone

Question :

I offer a three-Rak'ah prayer for Witr and I do not sit except in the last Rak'ah; and in the first Rak'ah, I recite a short Surah after Al-Fatihah, then in the second Rak'ah, I recite: "Say: "O you who disbelieve!"and in the third Rak'ah, I recite: "Say: "He is Allah, One." and Al- Mu'awwithatain. And sometimes, I pray eleven Rak'ahs as Witr and I do not sit until the last Rak'ah, and I recite the same Surahs which I mentioned, in the first three Rak'ahs and in the remainder of the Rak'ahs, I recite only Al-Fatihah. Is this prayer of mine correct, and how should I pray thirteen Rak'ahs?

When I miss the Maghrib prayer, the 'Isha' prayer or the Fajr prayer, I pray it alone, and I used to recite the Verses quietly to myself. Then I came to know from my uncle that it is obligatory to recite aloud in the audible prayers. Were my previous prayers correct? And is there any duty incumbent upon me?

Answer:

It is preferred to pray thirteen Rak'ahs or eleven Rak'ahs and to make the Taslim after every two Rak'ahs and to recite whatever you wish in every Rak'ah after Al-Fatihah. It is permissible to offer nine Rak'ahs, making the Taslim after every two Rak'ahs, or to perform eight Rak'ahs, then make the Tashahhud after them and then pray the ninth and make the Taslim at the end of it.

It is also permissible to offer seven Rak'ahs with single Taslim or five Rak'ahs with single Taslim, but it is preferred for the Witr to be no less than three Rak'ahs, reciting Sabbih in the first and in the third, Surah Al-Kafirun and Surah Al-Ikhlas, but if a person recites other than this, there is no objection. And it is preferred for the three Rak'ahs (of Witr) to be performed with two Taslims, but if they are performed with one Taslim, it is permissible, Allah willing

We say that there is no need to recite aloud when one is praying alone, because loud recitation in the night prayer is in order that those being led in prayer hear it and benefit from it; and a person praying alone hears himself, whether he recites aloud or not and therefore the desired objective is achieved.

Source:
Ibn Jibreen
Fatawa Islamiyah, Vol. 2 Pages 302-303