Nabil, who was asked by ‘Abdu’l-Bahá to select from the Writings of Bahá’u’lláh those passages which constitute the text of the Tablet of Visitation, which nowadays is usually recited in the Shrine of Bahá’u’lláh and the Báb, was inconsolable after the ascension of his Lord. To the ordeal of separation from his Beloved was added soon afterwards a far more grievous blow—the violation of the Covenant by ‘Abdu’l-Bahá’s brothers; which although it had not been made public at that time was clearly discernible to those who were close to the Holy Family. Nabil could no longer bear the agony of those cruel and tempestuous days. He took his own life by drowning himself in the sea a few months after the ascension of Bahá’u’lláh.
(Adib Taherzadeh, The Revelation of Bahá’u’lláh v 4, p. 418)