It is narrated from Sayyiduna Amr al-Yamani (may Allah be pleased with him); he said: The Prophet (peace and blessings be upon him) sent voluntary sacrificial animals with me and said: "If any of them breaks down (on the way, unable to go on), then slaughter it, then dip its sandal (hung on it as a mark) in its blood and strike it on its side, and leave it for the people (to eat)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14160