Musnad Ahmad 907:149

Abdullah narrated to us, Abu Bakr Khallad ibn Aslam narrated to me, al-Nadr ibn Shumayl narrated to us, Shu'bah narrated to us, from Simak, who said: I heard Abu Thawr ibn Ikrimah ibn Jabir ibn Samurah, from Jabir ibn Samurah, that the Prophet, peace and blessings of Allah be upon him, was asked about praying in sheep pens, and he granted a concession. He was asked about praying in camel pens, and he forbade it. He was asked about performing ablution (wudu) after eating camel meat, and he said: "Perform ablution." He was asked about performing ablution after eating sheep meat, and he said: "If you wish, perform ablution, and if you wish, do not."