The Prophet ﷺ drank some milk, then called for water, rinsed his mouth, and said, "It has greasiness to it."
إن النبي ﷺ شرب لبنا، ثم دعا بماء فمضمض وقال: إن له دسما.
Bukhari in wudu (211) and Muslim in Hayd (358), both from Qutayba bin Saeed, who said, "Layth narrated to us, from Aqeel, from Zuhri, from Ubaydullah bin Abdullah, from Ibn Abbas," and he related the hadith.As for what Ibn Majah reported (498) through Walid bin Muslim, who said, "Uzai narrated to us, from Zuhri, from Ubaydullah bin Abdullah bin Utba, from Ibn Abbas," that the Prophet ﷺ said, "Rinse your mouth after milk, for it has a fatty residue." This wording contains an irregularity, for all the others reported it as an action performed by the Prophet ﷺ, while Walid bin Muslim reported it as a command given by him. Walid engages in tadlis, but here he explicitly stated that he heard it directly, even though he differed from the trustworthy narrators in the wording of the hadith.