The Messenger of Allah ﷺ used to sacrifice two horned, white rams. He would mention the name of Allah and pronounce the takbir, and I saw him slaughter them with his own hand, placing his foot on their sides.
حدثنا هشيم أخبرنا شعبة عن قتادة
كان رسول الله ﷺ يضحي بكبشين أقرنين أملحين وكان يسمي ويكبر ولقد رأيته يذبحهما بيده واضعا على صفاحهما قدمه
Its isnad is sahih. It is found in Bukhari 7/130, in the chapter on sacrifices, the Prophet's ﷺ sacrifice, and Muslim 2/1506, no. 1966, in the chapter on the recommendation of sacrifice, and Abu Dawud 3/95, no. 2793, and Tirmidhi 4/84, no. 1494, who graded it hasan, and Ibn Majah 2/1043, no. 3120, and Darimi 2/103, no. 1945, all of them in the chapter on sacrifices, from Anas.