Musnad Ahmad 30:3735

Ali narrated to us, Warqa’ informed us, from Abu al-Zinad, from al-A’raj, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The Hour will not be established until a man passes by the grave of another man and says: 'Would that I were in his place,' not out of a desire to meet Allah."