PROPHET MUHAMMAD (ﷺ) said:
Whoever has an animal to sacrifice, when the crescent (1st) moon of Dhul-Hijjah appears, let him not remove anything from from his hair or nails, until he has offered sacrifice.

Narrated 'Ata bin Yasar:
"I asked Abu Abyub [Al-Ansari] how the slaughtering was done during the time of the Messenger of Allah (ﷺ). He said: 'A man would sacrifice a sheep for himself and the people in his household. They would eat from it and feed others, until the people (later) would boast about it and it became as you see now."