Musnad Ahmad 1167:61

'Affan narrated to us, he said: Hammad bin Zayd narrated to us, from Ayyub, from Ibn Abi Mulaykah, that Asma' said: I used to serve al-Zubayr, her husband, and he had a horse that I would tend to. There was no service more difficult for me than tending to the horse; I would gather fodder for it, look after it, tend to it, and crush date pits for it. She said: Then she obtained a servant, whom the Messenger of Allah (peace and blessings of Allah be upon him) gave to her. She said: So she relieved me of tending to the horse, and took the burden of it off me.