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 ‏.‏

Yahya related to me from Malik from Zayd ibn Aslam that hisfather said, "Abdullah ibn al-Arqam said, 'Show me a riding-camelwhich the amir al-muminim can give me to use.' I said, 'Yes. One ofthe sadaqa camels.' Abdullah ibn al-Arqam said, 'Would you want astout man on a hot day to wash for you what is under his lower garmentand its folds, and then give it to you to drink?' I was angry andsaid, 'May Allah forgive you! Why do you say such things to me?'Abdullah ibn al-Arqam said, 'Sadaqa is the impurities of people whichthey wash off themselves.' " Translation Not Available

Book Ref: Muwatta Imam Malik Book 58 Hadith 1858
Web Ref:  Muwatta Imam Malik Book 58 Hadith 15