Narrated Abu Huraira: 'I heard Allah's Messenger saying: "There were two fraternal persons among the Children of Israel. One of them was engrossed in committing sins while the other was devoted to worship. The devotee used to see his fellow committing sin and advise him: 'Desist from doing so.' One day when he found his fellow committing sin, he said to him: 'Avoid it.' He fellow said: 'Leave me alone. Have you been sent out as a vigilant on me?' The devotee said: 'By Allah, He will neither forgive you nor admit you to Paradise.' When they died, they were gathered before the Lord of the Worlds. Allah asked the devotee: 'Were you assured of knowing Me or were you having power over what was in My Hands?' Then He said to the sinner: 'Go and enter Paradise by My Mercy,' and ordered the angels about the devotee: 'Lead him to Hell.'"'
After narrating the Hadith, Abu Huraira commented: "By Him in Whose Hand my soul is: One word spoken by the devotee ruined his good deeds in the world as well as in the Hereafter."
-- From "110 Ahadith Qudsi: Sayings of the Prophet Having Allah's Statements"