September 26

There is no objection whatsoever to non-Bahá'ís being present when the long prayer for the dead is read, as long as they respect our manner of reading it by rising and standing as the Bahá'ís do on this occasion. Nor, indeed, is there any objection to non-Bahá'ís being present during the reading of any Bahá'í prayer for the departed. In reporting Bahá'í marriages it is much better to mention that the ceremony was performed by the Assembly, as this is the proper thing to do, and an individual only acts for the Assembly on this occasion. As a funeral is not a legal ceremony more latitude can be allowed, especially as the family of the deceased may want some particular Bahá'í friend to officiate.
. . .

Mr. and Mrs.... are naturally quite free to be buried in their own plot in the Cemetery, if that is what they desire.

An official Bahá'í funeral service should only be given for a believer, but there is no objection to the reading of Bahá'í prayers, or indeed to a Bahá'í conducting the funeral service of a non-Bahá'í, if this has been requested. 
- Shoghi Effendi  (From a letter dated 20 July 1946 written on behalf of Shoghi Effendi to the National Spiritual Assembly of the United States and Canada; The Compilation of Compilations, vol. I, Baha’i Burial)