Hadith 54
Chapter 9: Shortening the Prayer - كتاب قصر الصلاة فى السفر
Malik said, "I do not consider that his words, 'has not discharged anything' refer to anything other than the discharges that break wudu."
Reference Muwatta Malik 54
USC-MSA web (English) reference : Book 9, Hadith 54