Musannaf Ibn Abi Shaybah

Hazrat Abdur Rahman bin Ma'qal (may Allah have mercy on him) says that I was present in the gathering of Hazrat Ali (may Allah be pleased with him), when a man asked him: "What is the waiting period ('iddah) for a pregnant woman whose husband has passed away?" Hazrat Ali (may Allah be pleased with him) replied: "She will observe the longer of the two periods as her 'iddah." A man said: "Hazrat Abdullah bin Mas'ud (may Allah be pleased with him) gives the verdict that the 'iddah is completed upon delivery?" Hazrat Ali (may Allah be pleased with him) replied: "He does not know."