Praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Al-Awabeen means the righteous, those who celebrate the praises of Allah or the good doers. Ibn Abbas (May Allah be pleased with them) said: " They are those who celebrate the praises of Allah. He also said: "They are the obedient good doers." {Tafseer Ibn Atiah, Vol.3:P.449}.
Salatul Awabeen is the name given to two voluntary prayers:
First: Salatul Duha. The evidence is that Allah's Messenger (PBUH) said: "The prayer of those who are penitent is offered when the young weaned camels feel the heat of the sand." [Reported by Muslim].
Salatul Duha is a confirmed Sunnah, and it is two to eight Rakat. Anawawi said: "The author of the book "Al-Hawi" said: "Its preferred time is after the passage of one quarter of the day, because Allah's Messenger (PBUH) said: "The prayer of those who are penitent is offered when the young weaned camels feel the heat of the sand." [Reported by Muslim]." {Shareh Al-Mohathab, Vol.4:P.36}.
Second: The Salah that the Shafi jurists called Salatul Awabeen is the Salah performed between Maghrib and `Isha`. This is supported by the Hadith in which the Messenger of Allah (PBUH) said: ‘Whoever prays six Rak’ah after the Maghrib and does not speak evil between them, they will be made equivalent to twelve years’ worship.’” Also, the Hadithin which the Messenger of Allah (PBUH) said: 'Whoever prays twelve rak'ahs in a day apart from the obligatory prayers, Allah (SWT) will build for him, or there will be built for him, a house in Paradise.'" {Reported by Ibn Majah}.
This prayer is called the Salah/prayer of inattentiveness because people are occupied with their daily affairs, such as dinner, sleeping, and night chat. It was stated in the Shafi book {Hasheyat Al-Bajirmi Ala Al-Khateeb, Vol.1:P.427}: "The Salah of Al-Awabeen is called the Salah of inattentiveness because the people are busy having dinner or sleeping, and the like."
Although weak (Da`if), the Hadiths supporting Salatul Awabeen are to be acted upon because they celebrate an act of worship for which a Muslim is rewarded, this prayer is classified under voluntary prayers, and the companions as well as the Tabi`in used to perform it. For more information, check {Az-Zuhd War-Raqa`iq, Vol.1:P.445} by Ibn Mubarak and {Mosanaf Ibn Shaybah}. Salatul Awabeen is made of twenty Rakat at maximum and two Rakat at minimum, and it is included within other prayers performed at this time (Between Maghrib and `Isha`). It was stated in the Shafi book {Bushra Al-Karim, Vol.1:P.320}: "The complete form of Salatul Awabeen is twenty Rakat between Maghrib and `Isha`, and it is included within prayers performed at this time, according to Ar-Ramli, and its minimum is two Rakat."
Praying Salatul Awabeen (Salatul Duha or the Salah between Maghrib and `Isha`) in congregation isn`t a Sunnah. Kindly check the Shafie book {`Eanat At-Talibeen, Vol.1:P.299}. However, if performed in congregation, this Salah is valid.
It is from Sunnah to pray day prayers silently and night prayers aloud, because doing the opposite is disliked. Therefore, it isn`t permissible to pray Salatul Duha aloud because it is a day prayer. In addition, Saltul Awabeen between Maghrib and `Isha` is to be performed with moderate volume. According to scholars, praying silent prayer aloud and vice versa is disliked in Salah. Kindly Check {Shareh Al-Mohath-thab, Vol.3:P.391}.
In conclusion, observing Salatula Awabeen (Salatul Duha or the Salah between Maghrib and `Isha`) is amongst the righteous good deeds for which a Muslim is greatly rewarded, whether performed on permanent basis or not. And Allah the Almighty knows best