Following ‘Abdu’l‑Bahá’s instructions the remains were finally laid to rest in the Holy Land

…from whence [Imám-Zádih-Hasan in Tihrán] they were removed to different places, until the time when, in pursuance of ‘Abdu’l‑Bahá’s instructions, they were transferred to the Holy Land, and were permanently and ceremoniously laid to rest by Him in a specially erected mausoleum on the slopes of Mt. Carmel. 

- Shoghi Effendi  (Chapter 4, God Passes By)