"The Sunnah divorce is a divorce issued when she is pure (not menstruating) without having had intercourse with her. If she menstruates and becomes pure again, give her another divorce, and if she menstruates and becomes pure again, give her another divorce, then after that, she should wait for another menstrual cycle." (One of the narrators) Al-A'mash said: "I asked Ibrahim, and he said something similar." (Using translation from Nasāʾī 3394)  

أَنْ يُطَلِّقَهَا تَطْلِيقَةً وَهِيَ طَاهِرٌ فِي غَيْرِ جِمَاعٍ فَإِذَا حَاضَتْ وَطَهُرَتْ طَلَّقَهَا أُخْرَى فَإِذَا حَاضَتْ وَطَهُرَتْ طَلَّقَهَا أُخْرَى ثُمَّ تَعْتَدُّ بَعْدَ ذَلِكَ بِحَيْضَةٍ» قَالَ الْأَعْمَشُ سَأَلْتُ إِبْرَاهِيمَ فَقَالَ مِثْلَ ذَلِكَ  

"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)." (Using translation from Ibn Mājah 2020)  

أَنْ يُطَلِّقَهَا طَاهِرًا مِنْ غَيْرِ جِمَاعٍ»