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)." (DE)
English reference (DE): Vol. 3, Book 10, Hadith 2020 (DE)
Arabic reference (DE): Book 10, Hadith 2098 (DE)