How could the poisoned sheep affect the Prophet, peace and blessings be upon him, three years after he ate from it?

The death of the Prophet, peace and blessings be upon him, by poison is an established fact, and there is no difficulty in the death occurring years after he consumed it. This is because Allah protected him from immediate death and reserved for him his share of martyrdom to elevate his status. Thus, he would occasionally experience illness from that meal. The intensity of poisons varies among individuals, and the body may resist it. Bishr ibn al-Bara' died from the poison he ate with the Prophet, peace and blessings be upon him, some time before the Prophet. Poisons do not affect by themselves, but by the permission of Allah.