Surnamed Aqay-i-Kalim, he was a younger brother of Bahá’u’lláh who remained devoted and faithful to Baha'u'llah and served Him to the end of his life. After the Martyrdom of the Báb, Mirza Músá, at Bahá’u’lláh's instructions, hid the casket containing the remains of the Báb in the Shrine of Imam-Zadih Hasan in Tihran. Mirza Músá accompanied Bahá’u’lláh into exile and often served as His deputy in meeting with government officials and religious leaders, until 'Abdu'l-Baha took on this function. Shoghi Effendi designated him one of the Nineteen Apostles of Bahá’u’lláh. Mirza Músá died in 'Akka in 1887.
- Wendy Momen ('A Basic Baha'i Dicionary')