Acapella

Although acapella is technically defined as singing without instrumental accompaniment, it also refers to a group of people using their voices to emulate instruments. Shariah prohibits the use of musical instruments and listening to musical sounds. Therefore nasheed which contain musical instruments or vocals that emulate musical instruments will be impermissible.

Some Ulamaa have regarded it as tashabbuh bil fussaq (emulation of the transgressors) thereby falling under the Hadeeth:

من تشبه بقوم فهو منهم

Mulla Ali Qari rahimahullah mentions under this Hadeeth:

من تشبه بقوم، اي من شبه نفسه بالكفار مثلا في اللباس و غيره أو بالفساق أو الفجار أو بأهل التصوف و الصلحاء الابرار فهو
منهم في الاثم و الخير قال الطيي: هذا عام في الخلق و الخلق و الشعار
(مرقاة المفاتيح ٥/٨ ٢٥ كتاب اللباس)

The original purpose of permissible nasheeds and listening to them is:
1) To ignite and create the love of Allah within the hearts of the listeners.
2) To encourage people to follow the Sunnah of Rasulullah sallallahu alaihi wasallam .
3) To adorn the hearts of listeners with good qualities of Taqwa, Sabr, good character etc.
4) To enjoin good and forbid evil.
5) To create an aversion of sin within the hearts of people.

On the contrary, some of the present day so called nasheeds include:
1) Music.
2) Emulation of music.
3) The outward appearance of most of the present day nasheed artists is contrary to the message that they are conveying. Many do not practice on the Shariah and the Sunnah of Rasulullah sallallahu alaihi wasallam.
4) Pure entertainment and frivolity.
5) Tashabbuh of the fussaaq.

In conclusion, such nasheeds can never direct one to the true spirit of Deen and Shariah. The emotions experienced through such nasheeds are at most one’s imagination or supposed “closeness” to Deen, whereas they are far from the true spirit and purpose of Deen.