Musannaf Ibn Abi Shayba 1:1708

Abu Bakr narrated to us, he said: Isa ibn Yunus narrated to us, from Zam'ah ibn Salih, from Isa ibn Yazdad, from his father, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When one of you urinates, let him flick his private part three flicks."