Musannaf Ibn Abi Shayba 19:481

Muhammad ibn Abdullah ibn Yunus said: Abu Abd al-Rahman Baqi ibn Makhlad narrated to us. He said: Abu Bakr narrated to us, he said: Waki’ narrated to us, from Hisham, from Qatadah, from Sa’id ibn al-Musayyib, that a woman married during her waiting period (‘iddah), so Umar struck her as a discretionary punishment (ta’zir) less than the prescribed legal punishment (hadd).