Muwatta Imam Malik Book of Purity, Hadith 11

Yahya said that Malik said, "The situation with us is that one does not have to do wudu for a nose-bleed, or for blood, or for pus issuing from the body. One only has to do wudu for impurities which issue from the genitals or the anus, or for sleep."

قَالَ يَحْيَى: قَالَ مالِكٍ: «الْأَمْرُ عِنْدَنَا أَنَّهُ لَا يَتَوَضَّأُ مِنْ رُعَافٍ وَلَا مِنْ دَمٍ وَلَا مِنْ قَيْحٍ يَسِيلُ مِنَ الْجَسَدِ، وَلَا يَتَوَضَّأُ إِلَّا مِنْ حَدَثٍ يَخْرُجُ مِنْ ذَكَرٍ أَوْ دُبُرٍ أَوْ نَوْمٍ»