Musnad Abu Ya'la al-Mawsili 2:67

Husayn ibn al-Aswad al-Kufi narrated to us, Abu Usamah narrated to us, Hisham ibn Urwah narrated to us, from his father, from Ibn Umar, who said: I was present with my father when he was struck [mortally wounded]. They praised him with goodness, so he said: "A seeker of hope and a seeker of fear." They said: "Will you not appoint a successor?" He said: "Shall I bear your affair alive and dead? I wish that my portion from you is sufficiency—neither for me nor against me." Then he said: "If I appoint a successor, then one who was better than me appointed a successor [referring to Abu Bakr]. And if I leave you, then one who was better than me left you [referring to the Prophet], the Messenger of Allah, may Allah bless him and grant him peace." Abdullah ibn Umar said: So I knew, when he mentioned the Messenger of Allah, may Allah bless him and grant him peace, that he was not going to appoint a successor.