The Messenger of Allah ﷺ said, "The greatest of days before Allah is the Day of Sacrifice, then the Day of Departure."Five or six sacrificial camels were brought to the Messenger of Allah ﷺ for him to slaughter, and they began crowding toward him, each one trying to be the first. When their flanks fell to the ground, he uttered something quietly that I could not make out, so I asked one of those next to me, "What did he say?"They replied, "He said, 'Whoever wishes may cut off a portion.'"
حدثنا يحيى بن سعيد عن ثور قال حدثني راشد بن سعد عن عبد الله بن لحي
أن رسول الله ﷺ قال أعظم الأيام عند الله يوم النحر ثم يوم النفر وقرب إلى رسول الله ﷺ خمس بدنات أو ست ينحرهن فطفقن يزدلفن إليه أيتهن يبدأ بها فلما وجبت جنوبها قال كلمة خفية لم أفهمها فسألت بعض من يليني ما قال قالوا قال من شاء اقتطع
Its isnad is sahih. Rashid bin Saad Muqrai is trustworthy and has narrations in the Sunan works, and Abdullah bin Nujay has narrations that are considered reliable in the Sunan works as well. Hakim graded the hadith sahih (4/221) and Dhahabi agreed with him. It appears in Abu Dawud (2/148, no. 1765), in the chapters on rites, in the section on sacrificial animals that become disabled, and in Ibn Hibban (258, no. 1044, Mawarid).