Musnad Ahmad 30:3107

Waki' narrated to us, he said: Al-A'mash narrated to us, from 'Umarah ibn al-Qa'qa', from Abu Zur'ah, from Abu Hurairah, he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "O Allah, make the provision of the family of Muhammad only enough to sustain them."