Musnad Ahmad 8:4

Abu Amir narrated to us, Fulayh narrated to us, from Abdullah ibn Abd al-Rahman—meaning Ibn Ma’mar—who said: Amir ibn Sa’d narrated to Umar ibn Abd al-Aziz—while he was the governor of Medina—that Sa’d said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever eats seven Ajwa dates from between the two lava fields of Medina on an empty stomach, nothing will harm him that day until he reaches the evening." Fulayh said: And I think he said: "And if he eats them when he reaches the evening, nothing will harm him until he reaches the morning." Umar said: "Look, O Amir, at what you are narrating from the Messenger of Allah (peace and blessings of Allah be upon him)." He replied: "I bear witness that I did not lie about Sa’d, and Sa’d did not lie about the Messenger of Allah (peace and blessings of Allah be upon him)."