´It was narrated from Abu Salamah bin 'Abdur-Rahman that Zainab bint Abi Salamah told him, from her mother, Umm Salamah, the wife of the Prophet:` "That a woman from Aslam who was called Subai'ah was married to her husband, and he died while she was pregnant. Abu As-Sanabil bin Ba'kak proposed to her but she refused to marry him. He said: 'You cannot get married until you have observed 'Iddah for the longer of the two periods.' Approximately twenty days later she gave birth. She went to the Messenger of Allah and he said: 'Get married.'"
Hadith Referenceسنن نسائي / كتاب الطلاق / 3546
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح بخاري
From the apparent wording, it seems that Abu Sanabil sent the marriage proposal immediately after the death (of her husband), but this impression is not correct. In reality, he sent the proposal after the birth of the child. There has been advancement and delay (taqdim wa ta’khir) in the narration.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 3546
Narrated Um Salama: (the wife of the Prophet) A lady from Bani Aslam, called Subai'a, become a widow while she was pregnant. Abu As-Sanabil bin Ba'kak demanded her hand in marriage, but she refused to marry him and said, "By Allah, I cannot marry him unless I have completed one of the two prescribed periods." About ten days later (after having delivered her child), she went to the Prophet and he said (to her), "You can marry now."
Maulana Dawood Raz
Hadith Commentary:
Abu al-Sanabil misled the woman by telling her an incorrect ruling, causing her to delay her marriage so that her relatives and close ones who were not present at the time would arrive, and they would persuade her to agree to marry him.
There are two waiting periods (iddah): one is the period until childbirth, and the other is four months and ten days.
It was regarding this that Abu al-Sanabil gave his fatwa, whereas the waiting period (iddah) for a pregnant woman is only until childbirth, and nothing more.
Source: Sahih Bukhari: Commentary by Maulana Dawood Raz, Page: 5318