Explanation

 The event of "shaq al-sadr," the opening of the Prophet Muhammad's chest occurred four times.

The four instances are: 

1. During his childhood:

This is often mentioned as an early event, possibly related to the Prophet's early spiritual experiences.

2. At the age of ten:

This is another reported occurrence, possibly marking a stage in his development.

3. Upon being commissioned as a prophet:

This is linked to the beginning of his prophetic mission.

4. During the Miraj (ascension):

This is the final instance, which is a significant event in Islamic tradition.