Musnad Ahmad 30:1951

Yahya ibn Ishaq narrated to us, he said: Ibn Lahi'ah informed us, from Darraj Abu al-Samh, from Ibn Hujayrah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "By the One in Whose hand is my soul, everything will dispute on the Day of Resurrection, even the two sheep regarding what they butted each other for."