He invited Fadl to a meal on the day of Arafah, but Fadl said, "I am fasting."Abdullah said, "Do not fast. The Prophet ﷺ had a cup of milk brought to him on this very day and drank from it. The people follow your example."
أنه دعا الفضل يوم عرفة إلى طعام، فقال: إني صائم. فقال عبد الله: لا تصم، فإن النبي ﷺ قرب إليه حلاب فشرب منه هذا اليوم، وإن الناس يستنون بكم.
Imam Ahmad (2946) and Abu Yaala (2744) both narrated it through the hadith of Rawh, who said, Ibn Jurayj related to us, saying, Zakariya bin Umar informed me that Ata informed him that Abdullah bin Ibn Abbas called for (he then mentioned it). Its isnad is sahih. As for Ata, although he was not present at the event, since he did not meet Fadl, it appears that he heard it from Ibn Abbas.His saying, "hilab," with a kasrah on the ha, refers to the vessel in which milk is milked.