It is narrated from al-Sha'bi that a woman who had married during her 'iddah was brought to Umar bin al-Khattab (may Allah be pleased with him). He took her dowry and placed it in the public treasury, separated the two of them and said: These two may never come together, and this is their punishment. Al-Sha'bi said: Ali (may Allah be pleased with him) said: It is not like this; this is ignorance on the part of the people. Rather, they are to be separated, then she completes the remainder of her 'iddah from her first husband, then she begins another 'iddah. And Ali (may Allah be pleased with him) assigned her the dowry because of what was made lawful of her private parts. Al-Sha'bi said: Umar (may Allah be pleased with him) praised Allah and extolled Him, then said: O people, refer matters of ignorance back to the Sunnah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15545