Muwatta Imam Malik Book of Sadaqa, Hadith 15
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.' "
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ أَبِيهِ، أَنَّهُ قَالَ قَالَ عَبْدُ اللَّهِ بْنُ الأَرْقَمِ ادْلُلْنِي عَلَى بَعِيرٍ مِنَ الْمَطَايَا أَسْتَحْمِلُ عَلَيْهِ أَمِيرَ الْمُؤْمِنِينَ فَقُلْتُ نَعَمْ جَمَلاً مِنَ الصَّدَقَةِ . فَقَالَ عَبْدُ اللَّهِ بْنُ الأَرْقَمِ أَتُحِبُّ أَنَّ رَجُلاً بَادِنًا فِي يَوْمٍ حَارٍّ غَسَلَ لَكَ مَا تَحْتَ إِزَارِهِ وَرُفْغَيْهِ ثُمَّ أَعْطَاكَهُ فَشَرِبْتَهُ قَالَ فَغَضِبْتُ وَقُلْتُ يَغْفِرُ اللَّهُ لَكَ أَتَقُولُ لِي مِثْلَ هَذَا فَقَالَ عَبْدُ اللَّهِ بْنُ الأَرْقَمِ إِنَّمَا الصَّدَقَةُ أَوْسَاخُ النَّاسِ يَغْسِلُونَهَا عَنْهُمْ .