Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "When you mention the name (that is, say Bismillah), then also say Allahu Akbar." The narrator says: That is, do this when slaughtering an animal.
Al-Tabarani recorded it. Its chain contains a narrator, Uthman bin Abd al-Rahman al-Qurashi, and he is da'if (weak).