It was asked from Sayyiduna Ali (may Allah be pleased with him) that if someone committed adultery with his wife's sister, he replied: "His wife will not become forbidden for him, he should separate from his wife until the waiting period ('iddah) is over, then return to her, seek forgiveness from Allah, and not do such a thing again."
Hadith Referenceسنن سعید بن منصور / كتاب الطلاق / 2900
Hadith Gradingمحدثین:إسناده ضعیف
Hadith Takhrij«إسناده ضعیف، «انفرد به المصنف من هذا الطريق»» قال إبن حجر: محمد بن سالم ضعيف، قال الذھبی: متروک