It is narrated from Imam al-Sha'bi (may Allah have mercy on him) that Sayyiduna Ibn Umar (may Allah be pleased with them both) divorced his wife while she was menstruating, so Sayyiduna Umar (may Allah be pleased with him) came to the Prophet (peace and blessings be upon him),
and he (peace and blessings be upon him) ordered him that "he should take her back; then, if he thinks fit, he may divorce her while she is in a state of purity, at the start of her waiting period ('iddah)."