بُلُوغُ الْمَرَامِ
Bulugh al-Maram 1113
Marriage
وَعَنْ عَائِشَةَ رَضِيَ اَللَّهُ عَنْهَا قَالَتْ: { إِنَّمَا اَلْأَقْرَاءُ; اَلْأَطْهَارُ } . أَخْرَجَهُ مَالِكٌ فِي قِصَّةٍ بِسَنَدٍ صَحِيحٍ [1] .
Narrated 'Aishah (RA): al-Aqra' is the period of a woman's purity (which occurs between two menses). [Malik, Ahmad and an-Nasa'i reported it in the course of a story with a Sahih (authentic) chain of narrators].
Sunnah.com reference: Book 8, Hadith 176