Sayyiduna Anas (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "There is no 'aqr (slaughtering at the grave) in Islam." Abd al-Razzaq (may Allah have mercy on him) says: They (the Arabs) used to perform 'aqr at the grave, that is, slaughter a cow or the like.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 7069