Musnad Ahmad 1086:11

'Abd al-Samad narrated to us, Hisham narrated to us, from Yahya, from Muhammad ibn Ayyub, that a man from the Ansar narrated to him, who was called Muhayyisah. He had a cupper slave, and the Messenger of Allah (peace be upon him) forbade him from his earnings. He said: "Shall I not feed it to orphans of mine?" He said: "No." He said: "Shall I not give it as charity?" He said: "No." Then he granted him a concession to feed it to his water-carrying camel.