وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، أَنَّ تَفْسِيرَ، هَذِهِ الآيَةِ ‏{‏يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا قُمْتُمْ إِلَى الصَّلاَةِ فَاغْسِلُوا وُجُوهَكُمْ وَأَيْدِيَكُمْ إِلَى الْمَرَافِقِ وَامْسَحُوا بِرُءُوسِكُمْ وَأَرْجُلَكُمْ إِلَى الْكَعْبَيْنِ‏}‏ أَنَّ ذَلِكَ إِذَا قُمْتُمْ مِنَ الْمَضَاجِعِ ‏.‏ يَعْنِي النَّوْمَ ‏.‏ قَالَ يَحْيَى قَالَ مَالِكٌ الأَمْرُ عِنْدَنَا أَنَّهُ لاَ يَتَوَضَّأُ مِنْ رُعَافٍ وَلاَ مِنْ دَمٍ وَلاَ مِنْ قَيْحٍ يَسِيلُ مِنَ الْجَسَدِ وَلاَ يَتَوَضَّأُ إِلاَّ مِنْ حَدَثٍ يَخْرُجُ مِنْ ذَكَرٍ أَوْ دُبُرٍ أَوْ نَوْمٍ ‏.‏

Yahya related to me from Malik from Zaydibn Aslam that the ayat "You who believe! When you rise for prayerwash your faces, and your arms to the elbows, and wipe over your headsand your feet up to the ankles," refers to rising from bed, meaningsleep. Yahya said that Malik said, "The situation with us isthat one does not have to do wudu for a nose-bleed, or for blood, orfor pus issuing from the body. One only has to do wudu for impuritieswhich issue from the genitals or the anus, or for sleep." Translation Not Available

Book reference: Muwatta Imam Malik Book 2 Hadith 40
Web reference: Muwatta Imam Malik Book 2 Hadith 10