Musnad Ahmad 26:792

'Affan narrated to us, Qays narrated to us, al-A'mash informed us, from Ibrahim, from 'Ubaydah al-Salmani, from 'Abdullah ibn Mas'ud, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Indeed, some eloquence is magic, and the worst of people are those whom the Hour overtakes while they are alive, and those who take graves as places of worship."