Musnad Ahmad 30:2055

Mu'awiyah narrated to us, he said: Za'idah narrated to us, he said: 'Abdullah ibn Dhakwan, whose kunya is Abu al-Zinad, narrated to us, from 'Abd al-Rahman al-A'raj, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "O sons of 'Abd al-Muttalib, O sons of Hashim, purchase yourselves from Allah, the Mighty and Majestic. I possess no power to benefit you against Allah in anything. O mother of al-Zubayr, aunt of the Prophet, O Fatimah, daughter of Muhammad, purchase yourselves from Allah. I possess no power to benefit you against Allah in anything. Ask me for whatever you wish from my wealth."