Musnad Ahmad 30:183

Sufyan narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurairah, who attributed it to the Prophet (peace and blessings of Allah be upon him): "Is there not a man who would grant a household a she-camel, which goes out in the morning with a vessel [of milk] and returns in the evening with a vessel [of milk]? Indeed, its reward is great."