The Book of Divorce
27/2. Chapter:
The Sunnah Divorce
Sunan an-Nasai
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، عَنْ سُفْيَانَ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي الأَحْوَصِ، عَنْ عَبْدِ اللَّهِ، قَالَ طَلاَقُ السُّنَّةِ أَنْ يُطَلِّقَهَا طَاهِرًا فِي غَيْرِ جِمَاعٍ .
It was narrated that 'Abdullah said: "The Sunnah divorce is to divorce her when she is pure (not menstruating) without having had intercourse with her."
Reference : Sunan an-Nasa'i 3395In-book reference : Book 27, Hadith 7English translation : Vol. 4, Book 27, Hadith 3424