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They tried to poison him with food in prison several times, but it had no affect. The new Turkey saw him as a threat, he also had conversations with Atatürk, you can research it later.
The poisons didn't kill him, by the will of Allah swt, the poisons were remained and gathered in his upper part of his chest.
Highly known scholar in Turkey, and many Islamic groups reads his books in Turkey, and the most known Islamic group in Turkey called "Nurcu" is called after his name "Said Al-Nursi". The "Nurcu" group is very powerful in Turkey, and has alot of schools, highschools and universities both in Turkey and 100 other countries in the world (even in Denmark they have around 10 schools). And they further have one of the biggest TV channel "Samanyolu" in Turkey.
I hope this was an answer to your question.