Musannaf Ibn Abi Shayba 1:663

Ibn Mahdi narrated to us, from Hammad bin Zayd, from Ayyub, from Abu Qilabah, from Shaddad bin Aws: He said: If one of you becomes junub (ritually impure) at night, then wishes to sleep, let him perform wudu, for it is half of the janabah.