What is the obligation upon one who commits Zihār (unlawful association with one's wife) and does not find a slave to free?

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The consensus of scholars dictates that if the one committing Zihār cannot find a slave to free, his obligation is to fast for two consecutive months. This is based upon the statement of Allah the Almighty: {But whoever cannot find, then two months of consecutive fasting before they touch each other} (Quran 58:4), and the Hadith of Aws ibn al-Samit and Salama ibn Sakhr.