Imam Malik's Muwatta, Chapter: Sadaqa

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.' "