Musnad Ahmad 26:294

Mu'awiyah narrated to us, Za'idah narrated to us, from 'Asim ibn Abi al-Najud, from Shaqiq, from 'Abdullah, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Indeed, among the most evil of people are those whom the Hour will overtake while they are alive, and those who take graves as places of worship."