Theres also a hadeeth which states the first innovation was murder, by the son of Adam when he killed his brother, thats in Mishkaat ul-Masaabeeh
Salamun 'Alaykum Imaam Ghazali mentions it in his Ihyaa ulum ud-Deen. Aisha narrates that the first two innovations to appear was the usage of soap and overeating. It is also in one of the six collections. However, I do not think these come under the major innovations that makes one a bid'ah group. The major innovations are permitting the blood of Muslims to be halal, claiming the Qur'an was created, etc.
San'ani mentions that report in 'Subul alSalam', and he may source the report there. I'll have it checked by some scholar inshaAllah.
I am searching for the reference to this Hadeeth for a friend of mine. I recollect reading it on Sunniport. Narrated by the Mother of the Believers Sayiduna Ayesha Siddiqua Radiyallhu Anha ‘’The first Innovation that took place in the Ummah after Prophet Mohammed Sallallahualaihi Wa Sallam passed away was people began to eat their full. JazakAllahu Khayran