How Bahá’u’lláh was not killed after his assassination plot?
After Báb’s execution, Amir Kabir (then prime minister) who was aware of Baha’u’llah previous actions for the Bábi movement, announced that Mirzá Husayn-Ali Núri has damaged 25 million Rials to the treasury (half the cost of wars between Iran and Russia) and exiled him to Iraq. However after Amir Kabir was killed, Mirzá Husayn-Ali Núri returned to Iran and immediately plotted and aided an assassination on Nasser al-Din Shah (then King of Iran). The attempt was unsuccessful, leading to capturing many Bábis.
Oddly, all of Bábi prisoners were killed except Baha’u’llah! He had a guardian angel from Russia which told the prime minister that Baha’u’llah is a trust of Russia and no harm should come to him.
Iran had to exile him and his brother to Iraq.