It is narrated from Abu al-Sanabil bin Ba'kak (may Allah be pleased with him); he said: Sayyidah Subay'ah (may Allah be pleased with her) gave birth twenty-three or twenty-five (days) after the death of her husband. Then, when she became pure from her postnatal bleeding, she desired to marry. This was mentioned to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "If she wishes to do so, her waiting period ('iddah) has been completed."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14149