Musnad Ahmad 32:951

Waki’ narrated to us, from Shu’bah, from Qatadah; and Ibn Ja’far narrated to us, Shu’bah said: I heard Qatadah, from Anas, "That the Messenger of Allah (ﷺ) used to sacrifice two horned, black-and-white rams." He said: "And I saw him slaughtering them with his own hand." He said: "And I saw him placing his foot upon their sides, and he mentioned the name of Allah and said the Takbir."