Musnad Ahmad 1153:2314

Ya'qub narrated to us, Ibn Akhi Ibn Shihab narrated to us, from his uncle, who said: 'Urwah ibn al-Zubayr informed me that he heard 'Aishah say: A Jewish woman entered upon me and said: "Are you aware that you will be tested in the graves?" She said: The Messenger of Allah (peace and blessings of Allah be upon him) heard that, and he was startled, then he said: "It is only the Jews who are tested." 'Aishah said: I remained for some nights after that, then the Messenger of Allah (peace and blessings of Allah be upon him) said: "Are you aware that it has been revealed to me that you will be tested in the graves?"