Sunan Ibn Majah, Volume 3, Book 10, Hadith 2020 (DarusSalam) ⓘ
It was narrated that Abdullah said: "Divorce according to the Sunnah means divorcing her when she is pure, ( i.e., not menstruating) and without having had intercourse with her (during that cycle)."
حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ سُفْيَانَ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي الأَحْوَصِ، عَنْ عَبْدِ اللَّهِ، قَالَ طَلاَقُ السُّنَّةِ أَنْ يُطَلِّقَهَا طَاهِرًا مِنْ غَيْرِ جِمَاعٍ .
also referenced under: Hadith 2020 (Reference) & Book 10, Hadith 2098 (In-Book)