Musnad Abu Ya'la al-Mawsili 160:148

Abu Musa Ishaq ibn Musa ibn Abdullah ibn Musa ibn Yazid al-Ansari narrated to us, Muhammad ibn Ismail ibn Abi Fudayk narrated to us, he said: Ibrahim ibn al-Fadl ibn Sulayman, the freed slave of Banu Makhzum, narrated to me, from al-Maqburi, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The battlefield of death is between sixty and seventy [years of age]."