It was narrated that Umm Salamah, the wife of the Prophet, said:
"The Messenger of Allah said: 'If you drink milk, then rinse your mouths, for there is some greasiness in it.'" (DE)
English reference (DE): Vol. 1, Book 1, Hadith 499 (DE)
Arabic reference (DE): Book 1, Hadith 538 (DE)