Musnad Ahmad 30:2638

Waki’ narrated to us, from Muhammad ibn Shurayk, who said: ‘Ata’ narrated to us, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Excellent are the thirty camels; one rides upon their noble one, one lends their equipment, one gives away their abundant milker, and one milks them on the day of their watering at their resting places."