The Reason for Obligation of Five Prayers at Five Specific Times

It was narrated by Al-Hussain ibn Abi al-Ala' from Imam Jafar ibn Muhammad Al-Sadiq عليه السلام that He said: "When Adam عليه السلام was sent down from Paradise, a black mark appeared on his face from his head to his feet. His sorrow and weeping over what had befallen him continued for a long time. Archangel Jibril عليه السلام came to him and said: 'O’ Adam, what makes you weep?' He said: 'This mark that has appeared on me.' Archangel Jibril عليه السلام said: 'Stand up, O’ Adam, and pray, for this is the time of the first prayer.' Adam stood and prayed, and the mark receded to his neck. Archangel Jibril عليه السلام came to him at the time of the second prayer and said: 'Stand and pray, O’ Adam, for this is the time of the second prayer.' Adam stood and prayed, and the mark receded to his navel. Archangel Jibril عليه السلام came again for the third prayer and said: 'O’ Adam, stand and pray, for this is the time of the third prayer.' Adam stood and prayed, and the mark receded to his knees. Archangel Jibril عليه السلام then came for the fourth prayer and said: 'O’ Adam, stand and pray, for this is the time of the fourth prayer.' Adam stood and prayed, and the mark receded to his feet. Archangel Jibril عليه السلام finally came for the fifth prayer and said: 'O’ Adam, stand and pray, for this is the time of the fifth prayer.' Adam stood and prayed, and the mark disappeared. Adam praised and thanked Allah سبحانه وتعالى, and Archangel Jibril عليه السلام said: 'O’ Adam, the example of your descendants in these prayers is like your example with this mark. Whoever among your descendants prays the five daily prayers, his sins will be removed just as this mark was removed from you.'"