Musannaf Ibn Abi Shayba 21:254

Al-Fadl ibn Dukayn narrated to us, Abu Mis'ar narrated to us, from Sa'id ibn Abi Sa'id al-Maqburi, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The supplication of the oppressed is answered, even if he is a wicked person, for his wickedness is upon himself."