Musnad Ahmad 1077:8

'Affan narrated to us, he said: I asked Hammad bin Zayd about Sadaqat al-Fitr, so he narrated to me from Nu'man bin Rashid, from al-Zuhri, from Ibn Tha'labah bin Abi Su'ayr, from his father, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Give a sa' of wheat, or a sa' of barley"—and Hammad was uncertain—"for every two, young or old, male or female, free or slave, rich or poor. As for your rich, Allah will purify him, and as for your poor, He will return to him more than what he gives."