Setting prayers to music - 6 February 1973

It is entirely proper to set prayers to music, and the friends are free to sing prayers in unison. Indeed, assuming that the music is appropriate and that the believers do not make a ritual out of it, it is highly praiseworthy for choirs to sing appropriate verses revealed by Bahá'u'lláh and the Master...

We would assume also that the friends will always keep in mind that whether read, chanted or sung, prayers should be uttered with proper sense of reverence." 

- The Universal House of Justice (From a letter to the National Spiritual Assembly of Australia, February 6, 1973; compilation: ‘Lights of Guidance’)