Musannaf Ibn Abi Shayba 28:14

Waki’ narrated to us, he said: Ibn Abi Dhi’b narrated to us, from Sa’id al-Maqburi, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "You will be eager for leadership, and it will become a source of regret and remorse. How excellent is the wet nurse, and how wretched is the one who weans."