Poison couldn’t affect the Imam
The famous jurisprudent of the Maliki School of jurisprudence of 5th century Hijri, Hadhrat Ibn ‘Abdul Barr (May Allah shower His Mercy on him) has related a Tradition:
Translation: It is narrated on the authority of Hadhrat ‘Umair bin Ishaq (May Allah shower His Mercy on him), he says: We were with Imam Hasan (May Allah be well pleased with him)…He said: I have been poisoned by deception many times, but never like this. It was the effect of this poison that I have spat out a piece of my liver. Out of astonishment, I took a stick and kept turning it over and over. Imam Hussain (May Allah be well pleased with him) said: Who poisoned you? Imam Hasan (May Allah be well pleased with him) asked: What will you do? Kill him? Imam Hussain (May Allah be well pleased with him) said: Yes!
Imam Hasan (May Allah be well pleased with him) said: Let it be. If it is the person I think, then Allah Most High will give the severest punishment. If it is not, I don’t want an innocent to be killed on my account. (Al Istiya’ab Fi Ma’arifati Ashaab)
The aforementioned incident is related in the same book on the authority of Hadhrat Qataadah (May Allah be well pleased with him) as well.
All the scholars agree that the miracles of the saints are a blessing of Prophethood. That Imam Hasan (May Allah be well pleased with him) was not affected by poisoning was the blessing of the miracle of the Holy Prophet (Sallallahu alaihi wa sallam). He was not affected by the poisoning of a Jewish woman.