Baha'u'llah was the spiritual return (raj'ah) of the Bab.

After his exile to Edirne in Rumelia in late 1863, and ten years after his withdrawal to Sulaymaniyyah, he began sending letters to Iran announcing that he was the spiritual return (raj'ah) of the Bab. In 1867 he broke decisively with Azal. In the following years the vast majority of all Babis gave their allegiance to Baha'u'llah, becoming Baha'is.

(Baha'u'llah and the Naqshbandi Sufis in Iraq, 1854-1856 By Juan Ricardo Cole)