Musnad Ahmad 907:119

Abdullah narrated to us, Muhammad ibn Sulayman Lawin narrated to me, Abu Awanah narrated to us, from Uthman ibn Mawhab, from Ja'far ibn Abi Thawr, from Jabir ibn Samurah, who said: I was sitting with the Prophet, peace and blessings of Allah be upon him, and they asked him, "Should we perform ablution after eating the meat of sheep?" He said, "If you wish, perform ablution, and if you wish, do not perform ablution." They said, "O Messenger of Allah, should we perform ablution after eating the meat of camels?" He said, "Yes, perform ablution." They said, "O Messenger of Allah, should we pray in the sheepfolds?" He said, "Yes." They said, "Should we pray in the resting places of camels?" He said, "No."