Chapter on Ritual Washings (Ghusl) and the Method of Performing Ghusl for Janabah (major impurity)

It is narrated from Muhammad ibn Ali ibn Mahbub, from Ahmad, from Ali ibn Mahbub, from Ahmad, from Ali ibn Saif, from his father, from al-Husayn ibn Khalid al-Sayrafi. He (Narrator) said: “I asked Abu al-Hasan al awwal (the First) عليه السلام, ‘Why has the ghusl (ritual purification) of Friday been made obligatory?’" Imam عليه السلام replied: "Indeed, Allah سبحانه وتعالى the Exalted has completed the obligatory prayer with the supererogatory prayer, and He سبحانه وتعالى completed the obligatory fasting with supererogatory fasting, and He سبحانه وتعالى completed the obligatory wudu (ablution) with the ghusl of Friday, to make up for any error, shortcoming, or forgetfulness therein."