Musnad Ahmad 30:2663

Yazid ibn Harun narrated to us, he said: Ibn Abi Dhi'b informed us, from al-Maqburi, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him, who said: "You will be eager for leadership, and it will become a regret and a sorrow on the Day of Resurrection. So, how excellent is the wet nurse, and how wretched is the weaner."