He does not feel that the friends should make a practice of saying grace or of teaching it to children. This is not part of the Bahá’í Faith, but a Christian practice, and as the Cause embraces members of all races and religions we should be careful not to introduce into it the customs of our previous beliefs. Bahá’u’lláh has given us the obligatory prayers, also prayers before sleeping, for travellers, etc. We should not introduce a new set of prayers He has not specified, when He has given us already so many, for so may occasions.
(Shoghi Effendi, Lights of Guidance, p. 459)