Musannaf Ibn Abi Shayba 30:79

Yazid ibn Harun narrated to us, from Sufyan ibn Husayn, from Ya'la ibn Muslim, from Mujahid, that Umar ibn al-Khattab recited upon the pulpit: "Gardens of Eden." He then said: "And do you know what the Gardens of Eden are? It is a palace in Paradise that has five thousand doors. At every door are twenty-five thousand of the wide-eyed houris. None shall enter it except a prophet—congratulations to the occupant of the grave (and he pointed to the grave of the Messenger of Allah, peace and blessings of Allah be upon him)—and a truthful one (congratulations to Abu Bakr), and a martyr." Then he said: "And how could Umar attain martyrdom?" Then he said: "By the One who brought me out of my house, He is indeed capable of driving it to me."