Musnad Ahmad 1153:1401

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from al-Ash'ath ibn Sulaym, from his father, from Masruq, from 'Aishah, that a Jewish woman entered upon her and mentioned the punishment of the grave. She said to her, "May Allah protect you from the punishment of the grave." 'Aishah asked the Messenger of Allah, peace and blessings of Allah be upon him, about the punishment of the grave, and he said, "Yes, the punishment of the grave is true." 'Aishah said, "I did not see the Messenger of Allah, peace and blessings of Allah be upon him, pray a prayer after that except that he sought refuge from the punishment of the grave."