by Imam Muslim, translation by Abdul Hamid Siddiqui , Volume: The Book of Zakat (Kitab Al-Zakat)
Chapter: BLESSING FOR HIM WHO PRESENTS SADAQA
'Abdullah b. Abu Aufa said that it was the common practice of the Mes- senger of Allah (may peace be upon him) that when the people brought to him sadaqa he blessed them: 0 Allah, bless them. So when Abu Aufa brought to him Sadaqa he (the Holy Prophet) said: 0 Allah, bless, the posterity of Abu Aufa.
This hadith has been narrated by Shu'ba with the same chain of transmitters (but with a slight variation of words, that he said): (0 Allah), bless them."