Chapter 20: Tribute, Spoils, and Rulership (Kitab Al-Kharaj, Wal-Fai' Wal-Imarah)
Narrated Ibn 'Umar: 'Umar said: I shall not appoint a successor, for the Messenger of Allah (ﷺ) did not appoint a successor. If I appoint a successor (I can do so), for Abu Bakr had appointed a successor. He Ibn 'Umar) said: I swear by Allah, he did not mention (anyone) but the Messenger of Allah (ﷺ) and Abu Bakr. So I learnt he would not equate anyone with the Messenger of Allah (ﷺ), for he did not appoint any successor.
Sunan Abi Dawud 2939