Hadith 5:699
'Umar ibn Ayyub narrated to us, from Ja'far, from al-Zuhri, who said: I asked him, "Does a man buy his own charity (sadaqah)?" He said: "He does not buy it from the charity collector until he (the collector) brings it out, and he does not buy it when he brings it out until it is mixed with many sheep."
حدثنا عمر بن أيوب عن جعفر عن الزهري قال سألته أيشتري الرجل صدقته فقال لا يشتريها من المصدق حتى يخرجها ولا يشتريها إذا أخرجها حتى تختلط بغنم كثير