The Prophet ﷺ said, "The ten are the ten days of the sacrifice, the odd is the Day of Arafah, and the even is the Day of Sacrifice."
حدثنا زيد بن الحباب حدثنا عياش بن عقبة حدثني خير بن نعيم عن أبي الزبير
عن النبي ﷺ قال إن العشر عشر الأضحى والوتر يوم عرفة والشفع يوم النحر
Its chain of transmission is sahih. Haythami said in 7/137, "Its narrators are the narrators of the Sahih, apart from Ayyash bin Uqbah, who is reliable." The hadith is found in Nasai in the tafsir of Surah Fajr, and likewise in Hakim, who graded it sahih, and Dhahabi agreed with him.