(6) باب نواقض الوضوء
Also reported by Abu Da'ud mentioning the above addition without the words "the string is untied", but both versions are weak. (ID)
Reference (ID): Bulugh al-Maram 81 (ID)
In-book reference (ID): Book 1, Hadith 98 (ID)
English translation (ID): Book 1, Hadith 87 (ID)