Hijra

In this timeline, Muhammad was assasinated in Mecca before he and his followers were able to escape to Medina.

POD
When Muhammad discovered that several prominent Meccan tribal leaders were plotting to assasinate him, he decided to join the majority of his followers who had under his guidance already migrated to Medina. With the help of Ali ibn Abd Munaf, he managed to trick to Meccans watching him and attempted to flee the city.

However, during this flight, Muhammad stumbled randomly into Sakhr ibn Harb and his guards as he neared the city's gate. In the insuing struggle, Muhammad was mobbed by Sakhr's guards and murdered.

After Effects
The Muslims in Medina, upon hearing of the death of their prophet, fell into a deep mourning. While they continued to declare Muhammad a prophet and a martyr, they fell into deep disfavour with both the Medinan Jewish community, which they had previously viewed as natural allies due to being a similarly Abrahamic religion, and the local pagan clans. Within a few years, most of them had dispersed, and by 63, little remained of Islam.

In 683, Ali ibn Harb managed to subjugate all opposing tribes in Mecca and formally converted to Christianity to secure an alliance with the Byzantine Empire.