What were the changes that occurred in Muslim rituals after Muhammad's death?

Ashura of Muharram - A Shia and Sunni Muslim Observance | IqraSense.com (http://www.iqrasense.com/islamic-history/ashura-of-muharram-a-shia-and-sunni-muslim-observance.html)
You could be looking for the history of the Shia-Sunni split.
The Origins of the Sunni/Shia split in Islam (http://www.islamfortoday.com/shia.htm)

There should be NO changes in Islam after our prophet death, if there is a change occurred, it called bid'ah and should not be followed. All bid'ah(innovations) are misleading and will the people that do bid'ah shall go to hell. (See: hadith Muslim)

There should be NO changes in Islam after our prophet death, if there is a change occured, it called bid'ah and should not be followed. All bid'ah(innovations) are misleading and will the people that do bid'ah shall go to hell. (See: hadith Muslim)

Assalaam alaikum,

It is true there shouldn't be any changes,but the sad truth is there have been changes and many are misguided in their devotions.
Insha Allah the ones who try to stay on the true path against all odds Insha Allah will have the best of rewards.

Wa alaikum salaam