It is narrated from Masruq that Umar (may Allah be pleased with him) said concerning a woman who marries during her 'iddah: Her marriage is unlawful and her dowry is unlawful. He ordered that her dowry be placed in the public treasury (bayt al-mal) and said: These two may never come together as long as they live.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15542