Musannaf Ibn Abi Shayba 1:893

Ibn Idris narrated to us, from Hisham, from al-Hasan, regarding the person in a state of major ritual impurity (junub) who puts his hand into a vessel before washing it, or a man who wakes up from his sleep and puts his hand into a vessel before washing it: He said: If he wishes, he may perform ablution (wudu), and if he wishes, he may pour it out.