Musnad Ahmad 907:203

Hashim narrated to us, Shaiban narrated to us, from al-Ash'ath, from Ja'far ibn Abi Thawr, from Jabir ibn Samurah, who said: "The Messenger of Allah, peace and blessings of Allah be upon him, commanded us to perform ablution (wudu) after eating camel meat, and not to perform ablution after eating mutton. And he commanded us to pray in sheep pens, and not to pray in camel resting places."