He saw the Prophet ﷺ slaughter his sacrificial animal with his own hand, saying the takbir over it.
حدثنا يونس حدثنا أبان يعني ابن زيد العطار عن قتادة
أنه رأى النبي ﷺ ذبح أضحيته بيده وكان يكبر عليها
Its chain of transmission is sahih. Muslim narrated it 3/1556, no. 1966, in the chapter on udhiya, on the recommendation of udhiya. Abu Dawud narrated similarly 3/95, no. 2794. Tirmidhi narrated it 4/84, no. 1494, in the chapter on offering udhiya with two rams, and said, hasan sahih. Nasai narrated similarly 7/220, no. 4387, and Ibn Majah 2/1043, no. 3120.