It is narrated from Sayyiduna Abdullah (may Allah be pleased with him) concerning the verse "Then divorce them for their waiting period" that he said: "Whoever wishes to give a divorce (in its true sense), let him give the woman time until, when she becomes pure from menstruation (and in that state) he has not had intercourse with her, he says to her: 'Count your waiting period.' Then if he regrets it and his heart longs for her, let him take two men as witnesses to his taking her back; otherwise, let him leave her until her waiting period is completed. And let him not give her three divorces while she is pregnant, or else Allah will make him regret it, and (in that state) he will have to bear the expenses of her pregnancy and her nursing."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9580