Musannaf Ibn Abi Shayba 9:892

Muhammad ibn Bishr narrated to us, from Sa'id, from Qatadah, from Sa'id ibn al-Musayyib, Jabir ibn 'Abd Allah, and Sa'id ibn Jubayr, regarding the man who commits adultery with a woman and then marries her: They said: There is no harm in that if they both repent and reform.