Yahya related to me from Malik from Zayd ibn Aslam that his
father said, "Abdullah ibn al-Arqam said, 'Show me a riding-camel
which the amir al-muminim can give me to use.' I said, 'Yes. One of
the sadaqa camels.' Abdullah ibn al-Arqam said, 'Would you want a
stout man on a hot day to wash for you what is under his lower garment
and its folds, and then give it to you to drink?' I was angry and
said, 'May Allah forgive you! Why do you say such things to me?'
Abdullah ibn al-Arqam said, 'Sadaqa is the impurities of people which
they wash off themselves.' "
Muwatta Malik Book 58, Hadith 15