Yahya related to me from Malik from Nafi that Abdullah ibn Umarwas asked about a woman whose husband died while she was pregnant, andhe said, "When she gives birth, she is free to marry." A man of theAnsar who was with him told him that Umar ibn al-Khattab had said,"Had she given birth while her husband was still on his bed, unburied,she would be free to marry."
USC-MSA web (English) reference: Book 29, Hadith 84
Arabic reference: Book 29, Hadith 1247