Musnad Ahmad 1153:2002

Yazid narrated to us, Hajjaj informed us, from Qatadah, from Safiyyah bint Shaybah, from Aisha, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, for every people there is a source of support (maddah), and the source of support for Quraysh is their freedmen (mawali)."