~Age 8, c. 578 CE
Details differ across the sources
The hadith giving the Prophet ﷺ's exact age (8) at Abdul Muttalib's death is graded slightly weak, though it is generally relied upon for the chronology.
At age eight, the Prophet ﷺ became an orphan for the third time when his grandfather Abdul Muttalib, by then old and blind, passed away. On his deathbed, Abdul Muttalib entrusted the Prophet ﷺ to his son Abu Talib, the full brother of Abdullah, the Prophet ﷺ's father.
Abu Talib took charge of the Prophet ﷺ and lived a long life, passing away when the Prophet ﷺ was over fifty years old.
Watch over Muhammad ﷺ as your own, for you are the full brother of his father Abdullah.
Passed away at an advanced age, having gone blind in his final years, leaving Muhammad ﷺ an orphan for the third time.
Yes, I remember him. And I was 8 years old when he died.
Said in answer to a companion who asked whether he remembered Abdul Muttalib.
“So that you may be raised under My care”
Cited (with 20:41) as a parallel to Musa AS being providentially raised without his birth parents, in answer to why the Prophet ﷺ was made an orphan three times over by this point in his life.
“And I chose you for Myself”
Cited (with 20:39) as a parallel to Musa AS being chosen and providentially raised, in answer to why the Prophet ﷺ was made an orphan three times over by this point in his life.