Musnad Ahmad 27:1746

Mu'awiyah ibn 'Amr narrated to us, Za'idah narrated to us, from 'Ata', from Muharib ibn Dithar, from 'Abdullah ibn 'Umar, from the Prophet, may Allah bless him and grant him peace, that he said: "O people, fear injustice, for it is darknesses on the Day of Resurrection."