Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates: A man asked the Prophet (peace and blessings be upon him): What is your view about a man who forgets to say Bismillah while slaughtering an animal? The Prophet (peace and blessings be upon him) said: The name of Allah is on the mouth of every Muslim.
Al-Tabarani recorded it in al-Mu'jam al-Awsat. Its chain contains a narrator, Marwan bin Salim al-Ghifari, and he is matruk (abandoned).