From Sahih Muslim (Hadith 5102):
Ibn 'Umar reported that Allah's Messenger (ﷺ) forbade that the flesh of sacrificial animals be eaten beyond three (days) Salim (son of Ibn Umar) said:Ibn 'Umar did not eat the flesh of the sacrificial animals beyond three (days). Ibn Abu 'Umar said:" Beyond three days
Reference: Muslim 5102