June 26. On this date in 1936, a letter written on behalf of Shoghi Effendi to an individual believer, "Regarding your question as to the meaning of Jin or Genii referred to in the Qur'an, these are not beings or creatures that are actually living, but are symbolic references to the power of men of evil and may be likened to evil spirits. But the point to bear in mind is that these have no positive existence of any kind."

June 26. On this date in 1936, a letter written on behalf of Shoghi Effendi to an individual believer, "Regarding your question as to the meaning of Jin or Genii referred to in the Qur'an, these are not beings or creatures that are actually living, but are symbolic references to the power of men of evil and may be likened to evil spirits. But the point to bear in mind is that these have no positive existence of any kind."

1667. Meaning of "Jin" or "Genii"
"Regarding your question as to the meaning of Jin or Genii referred to in the Qur'an, these are not beings or creatures that are actually living, but are symbolic references to the power of men of evil and may be likened to evil spirits. But the point to bear in mind is that these have no positive existence of any kind."
(From a letter written on behalf of the Guardian to an individual believer, June 26, 1936: Bahá'í News, No. 105, p. 1, February 1937)

On June 3, 1955,  Shoghi Effendi addressed a cablegram titled "Archbreaker of Bahá'u'lláh's Covenant" where he mentions that 'Abdu'l-Bahá, in reference to Mirza Majdi'd-Din, was "denounced by Him as the incarnation of Satan."

Majdi'd-Dín was the son of Bahá’u’lláh's full brother Áqáy-i-Kalím, also known as Mirzá Musa.  Majdi'd-Dín was married to Samadiyyih, Bahá’u’lláh's daughter from his second wife Fatimih Khanum, who Bahá’u’lláh titled Mahd-i-'Ulya. Both Majdi'd-Dín and Samadiyyih were eventually declared Covenant-breakers.

Mirza Majdi'd-Din for a time transcribed the Tablets of Bahá'u'lláh, but later became "the most redoubtable adversary of 'Abdu'l-Bahá" by supporting Mírzá Muhammad `Alí, the arch-breaker of the Covenant. Mirza Majdi'd-Din was the one who read the Kitáb-i-'Ahd in front of the family upon the death of Bahá'u'lláh.   Mirza Majdi'd-Din died at the age of 100 after suffering a stroke.

Archbreaker of Bahá'u'lláh's Covenant
Announce to National Assemblies that Majdi'd-Din, the most redoubtable adversary of 'Abdu'l-Bahá, denounced by Him as the incarnation of Satan and who played a predominant part in kindling the hostility of `Abdu'l-Hamid and Jamál Páshá, and who was the chief instigator of Covenant-breaking and archbreaker of Bahá'u'lláh's Covenant, and who above sixty years labored with fiendish ingenuity and guile to undermine its foundations, miserably perished struck with paralysis affecting his limbs and tongue. Dispensation of Providence prolonged the span of his infamous life to a hundred years, enabling him to witness the extinction of his cherished hopes and the disintegration with dramatic rapidity of the infernal crew he unceasingly incited and zealously directed, and the triumphant progress and glorious termination of 'Abdu'l-Bahá's thirty-year ministry as well as evidences of the rise and establishment in all continents of the globe of the administrative order, child of the divinely-appointed Covenant and harbinger of the world-encircling order.
--Shoghi
[Cablegram, June 3, 1955]