Musannaf Ibn Abi Shayba 1:1463

Isma'il ibn 'Ayyash narrated to us, from 'Abd al-'Aziz ibn 'Ubayd Allah, who said: I heard al-Sha'bi saying: "Wudu is obligatory from every dripping blood." He said: And I heard al-Hakam saying: "From every flowing blood." Abu Bakr said: I heard Ibn Idris saying: I heard Malik ibn Anas saying: "There is no wudu except from the two passages: excrement and urine."