The sunnah form of divorce is to divorce her while she is in a state of purity without having had intercourse with her.
حدثنا محمد بن بشار حدثنا يحيى بن سعيد عن سفيان عن أبي إسحق عن أبي الأحوص
طلاق السنة أن يطلقها طاهرا من غير جماع
[Hasan] Reported by Nasai, Divorce, chapter on divorce according to the sunnah, no. 3424, from the hadith of Yahya Qattan through this route. Ibn Hazm graded it sahih in Al-Muhalla, 10/172, issue 1949. See no. 46 for its underlying flaw. The hadith has corroborating narrations in Ibn Abu Shayba, Book of Divorce, chapter 1, and elsewhere.