The Imams عليه السلام know when they will die and they die voluntarily

7. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from al-Washsha’ from Ahmad ibn ‘Aidh from abu Khadija from abu ‘Abdallah عليه السلام who has said the following. “I was in the presence of my father during the day in which he passes away. He made several recommendations to me about his funeral matters, such as washing his whole body, shrouding him and placing him in his grave. I then said to him, “Father, I have not seen in a better health from the day you complained illness than today. I do not see in you any sign of death.” The Imam عليه السلام said, “Son, have you not heard about Ali ibn al-Husayn عليه السلام calling from behind the wall, ‘O Muhammad, come. Be quick.’”