You have asked whether it is permissible for the friends to chant a prayer collectively. There is a difference between chanting a prayer collectively and congregational prayer. The latter is a formal prayer usually led by an individual using a prescribed ritual. Congregational prayer in this form is forbidden in the Faith except in the case of the Prayer for the Dead. While reciting prayers in unison and spontaneously joining in the recitation of the Words of God is not forbidden, the friends should bear in mind the advice of the beloved Guardian on this subject when he stated that:
“although the friends are thus left free to follow their own inclination, ... they should take the utmost care that any manner they practice should not acquire too rigid a character, and thus develop into an institution. This is a point which the friends should always bear in mind, lest they deviate from the clear path indicated in the Teachings." [Synopsis and Codification of the Kitáb-i-Aqdas]
- The Universal House of Justice (From a letter written on behalf of the
Universal House of Justice to an individual believer, dated 6 February 1975;
The Compilation of Compilations, vol. I, Extracts on Baha’i Burial)