Sulayman bin Yasar (may Allah have mercy on him) relates that Sayyiduna Abu Hurayrah and Sayyiduna Ibn Abbas (may Allah be pleased with them) and Abu Salamah (may Allah have mercy on him) gathered and discussed the woman who gives birth after the death of her husband. Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: (Her waiting period is) whichever of the two terms ends later. Abu Salamah (may Allah have mercy on him) said: When she gives birth, she becomes lawful (for marriage). Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: I side with my nephew. So they sent Kurayb to Sayyidah Umm Salamah (may Allah be pleased with her), and she related the hadith of Subay'ah (may Allah be pleased with her): that the Prophet (peace and blessings be upon him) had ordered her to marry.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19876