Sahih Bukhari Volume 003, Book 047, Hadith Number 786.
Narated By Anas bin Malik : A Jewess brought a poisoned (cooked) sheep for the Prophet who ate from it. She was brought to the Prophet and he was asked, "Shall we kill her?" He said, "No." I continued to see the effect of the poison on the palate of the mouth of Allah's Apostle.