I asked the Messenger of Allah ﷺ about the day of the greatest pilgrimage, and he said, "It is the Day of Sacrifice."
حدثنا عبد الوارث بن عبد الصمد بن عبد الوارث حدثنا أبي عن أبيه عن محمد بن إسحق عن أبي إسحق عن الحارث
سألت رسول الله ﷺ عن يوم الحج الأكبر فقال يوم النحر
[Sahih] Ibn Abu Hatim also narrated it in his Tafsir (6/1747, Tawbah 3) through Abdul-Warith bin Saeed, with the same wording. Its chain is daif due to defects, but it has corroborating narrations in Bukhari, no. 3179, and Muslim, no. 1347/435, and others.