Musnad Ahmad 27:177

Abu Mu'awiyah narrated to us, Muhammad ibn Suqah narrated to us, from Abu Bakr ibn Hafs, from Ibn Umar, who said: A man came to the Messenger of Allah, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, I have committed a great sin, so is there any repentance for me?" The Messenger of Allah, peace and blessings of Allah be upon him, said to him: "Do you have parents?" He said: "No." He said: "Do you have a maternal aunt?" He said: "Yes." The Messenger of Allah, peace and blessings of Allah be upon him, said: "Then be dutiful to her."