According to search-discovered classical Islamic scholarship, the act of fasting for two consecutive months (ṣiyām shahrayn mutatābi'ayn) is a major, prescribed expiation (kaffarah) for specific grave sins. As detailed in Quran 58:4, this ruling serves as the second option of penance for the pre-Islamic practice of zihar, required when one cannot free a slave. Classical jurists like Al-Qurtubi and Ibn Kathir affirm its application to other major sins as well, such as unintentional killing or deliberately breaking a Ramadan fast with intercourse. The core of the ruling, emphasized by all scholars, is the term 'mutatābi'ayn' (consecutive), which mandates an uninterrupted sixty-day fast. This stringent condition underscores the seriousness of the sin and the depth of repentance required, making it a profound act of spiritual discipline and legal restitution before Allah. The only permissible breaks are for valid Shar'i excuses, after which the fast must be resumed. This Divine legislation replaces arbitrary and unjust customs with a structured path to forgiveness and reconciliation.