Musnad Ahmad 30:1842

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Sa‘d ibn Ibrahim, from Abu Salamah, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "While a man was riding a cow, it turned toward him and said: 'I was not created for this; I was only created for plowing.'" He said: "Then I believed in it, as did Abu Bakr and ‘Umar." He said: "And a wolf took a sheep, so the shepherd followed it. The wolf said: 'Who will take care of it on the day of the wild beasts, the day when it has no shepherd other than me?'" He said: "Then I believed in it, as did Abu Bakr and ‘Umar." Abu Salamah said: "And neither of them (Abu Bakr and ‘Umar) were among the people at that time."