Sunan Ibn Majah, Book 1, Hadith 537 (In-Book) ⓘ
It was narrated from Ibn 'Abbas that: The Prophet said: 'Rinse your mouths after drinking milk for there is some greasiness in it."
حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ إِبْرَاهِيمَ الدِّمَشْقِيُّ، حَدَّثَنَا الْوَلِيدُ بْنُ مُسْلِمٍ، حَدَّثَنَا الأَوْزَاعِيُّ، عَنِ الزُّهْرِيِّ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ بْنِ عُتْبَةَ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ النَّبِيَّ ـ صلى الله عليه وسلم ـ قَالَ " مَضْمِضُوا مِنَ اللَّبَنِ فَإِنَّ لَهُ دَسَمًا " .
also referenced under: Hadith 498 (Reference) & Volume 1, Book 1, Hadith 498 (DarusSalam)