Abdul Baha introduces as an obligatory practice ziyara to the shrine of Baha'u'llah

With the death of Baha' Allah in 1892, his tomb at Bahji near Acre was designated by 'Abd al-Baha' as a place of ziyara ranking in importance with the houses in Shiraz and Baghdad. In one letter, he writes that "there is no obligation for everyone to visit such places [holy sites in general], other than the three, namely: the Most Holy Shrine, the Blessed House in Baghdad and the venerated House of the Bab in Shiraz. To visit these is obligatory if one can afford it and is able to do so, and if no obstacle stands in one's way ... These three Holy Places are consecrated to pilgrimage." It should, however, be made clear that what 'Abd al-Baha' is here referring to is ziyara; hajj as such, with its connected rites, may only be performed to the two houses, even though this cannot be done in practice. 'Abd al-Baha's statement is interesting in that it permits ziyara as well as hajj to the houses, and introduces as an obligatory practice ziyara to the shrine of Baha' Allah.

(Rituals in Babism and Baha'ism by Denis MacEoin, London: British Academic Press, 1994)

https://bahai-library.com/maceoin_rituals_babism_bahaism