The Angels of Death:

اللَّهُ يَتَوَفَّى الْأَنْفُسَ حِينَ مَوْتِهَا ... [1]

“Allah takes the souls at the time of their death,” In this verse God makes Himself the reference of “taking the souls of the people.” But in the following verse “taking the people’s soul” refers to the Angel of Death:

قُلْ يَتَوَفَّاكُمْ مَلَكُ الْمَوْتِ الَّذِي وُكِّلَ بِكُمْ  [2]

“Say: The angel of death who is put in charge of you shall cause you to die,” and in the following verse “the taking of the people’s souls” is ascribed to the dispatched angels:

...حَتَّى إِذَا جَاءَ أَحَدَكُمْ الْمَوْتُ تَوَفَّتْهُ رُسُلُنَا وَهُمْ لَا يُفَرِّطُونَ  [3]

“Until when death comes to one of you, Our messengers cause him to die, and they are not remiss.”

In the book called Tauhid, Imam Sadiq(a.s) is reported to have said: “The angel of Death was once asked: How would you receive the souls at one moment while some of them are in the east and some are in the west? The Angel of Death replied: I call these souls and they will obey. Then Imam Sadiq(a.s) continued: the world is in my hand such as a bowl is in yours. Whatever you want, you will eat from it. And the world to me is like a Dirham: I can turn it however I wish.

When some body was casting doubt over these verses, Imam Sadiq(a.s) stated: God the Almighty, has appointed some associates for the Angel of Death who cause people to die.[4]