Through this chain of narration, from Muhammad ibn Ya’qub, from a group of our companions, from Ahmad ibn Muhammad, from Ali ibn Saif, from his father, Saif ibn Umayrah, from al-Husayn ibn Khalid, who said: I asked Abu al-Hasan al-Awwal عليه السلام: 'Why is the ghusl of Friday considered obligatory?' Imam عليه السلام said: 'Allah سبحانه وتعالى, completed the obligatory prayer with the supererogatory prayer, completed the obligatory fasting with supererogatory fasting, and completed the ablution for supererogatory acts with the ghusl of Friday to compensate for any oversight, shortcoming, or deficiency in them.'"