How was Hamza born four years before the Prophet, even though Abdullah and Abd al-Muttalib got married on the same day, and Amina became pregnant with the Prophet after Abdullah's death?

The fraternal relationship between the Prophet (peace be upon him) and Hamzah ibn Abd al-Muttalib through fosterage is agreed upon and established in the two Sahih collections, as both were nursed by Thuwaybah, Abu Lahab's freed slave-woman. As for the statement that Abd al-Muttalib and Abdullah married on the same day, it is incorrect due to the weakness of the narrations in which it was mentioned.

Regarding Hamzah being two or four years older than the Prophet (peace be upon him) despite sharing fosterage, some scholars are of the view that Hamzah was not older than the Prophet, while others believe that fosterage does not necessitate simultaneity. Thuwaybah might have nursed Hamzah first, then nursed the Prophet later, while maintaining the age difference.

Whatever the case, these historical matters do not give rise to doubt concerning creed or practice.