Abdullah bin Umar reported,
He divorced his wife while she was menstruating, so this was mentioned to Umar. Umar went to the Messenger of Allah ﷺ and informed him.The Messenger of Allah ﷺ said, "Let him keep her until she completes this menstrual period, then has another, then becomes pure. If he then wishes to divorce her, let him divorce her as Allah 
has commanded, and if he wishes to keep her, let him keep her."
Ahmad 5270
Sahihحدثنا روح حدثنا محمد بن أبي حفصة
حدثنا ابن شهاب عن سالم عن أبيه
أنه طلق امرأته وهي حائض فذكر ذلك إلى عمر فانطلق عمر إلى رسول الله ﷺ فأخبره فقال رسول الله ﷺ ليمسكها حتى تحيض غير هذه الحيضة ثم تطهر فإن بدا له أن يطلقها فليطلقها كما أمره الله عز وجل وإن بدا له أن يمسكها فليمسكها
Its isnad is sahih, and this is also one of the narrations of the story of Ibn Umar, which will come again later with this same isnad at 5525. It is worth pointing out here, for the sake of completeness, the numbers of the hadiths in the Musnad that contain this story, which are 4500, 4789, 5025, 5121, 5164, 5228, 5268, 5270, 5272, 5299, 5321, 5434, 5489, 5504, 5524, 5525, 5792, 6061, 6119, 6141, 6246, 6329.