It is narrated from Umar, Abdullah and Abu Musa (may Allah be pleased with them) concerning a man who divorced his wife, then she menstruated, and when she reached the third menstruation he took her back before she had bathed. They said: He is more entitled to her as long as she has not taken the bath from the third menstruation.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15397