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