What is the legal basis from the Qur'an and Sunnah that permits the intermingling of men and women during Tawaf in the Hajj season?

Islam does not permit the mixing of men and women during Tawaf if there is a fear of temptation (fitna), due to the corrupting effects that may result from it. It is reported from Umm Salama (may Allah be pleased with her) that she performed Tawaf from behind the people while riding, so as to be more modest for her. And Aisha (may Allah be pleased with her) used to perform Tawaf separately from men. The mixing that now occurs around the Kaaba is not an evidence for its permissibility, and if a circumambulator is compelled to mix, he must avoid touching women and looking at them.