Musannaf Ibn Abi Shayba 33:1018

Ghundar narrated to us, from Muhammad bin Ja'far, from Shu'bah, from 'Amr bin Murrah, from 'Abdullah bin al-Harith, from Abu Kathir al-Zubaydi, from Ibn 'Amr, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Beware of injustice, for injustice is darknesses on the Day of Resurrection."