Jami` at-Tirmidhi 1194

Sulaiman bin Yasir narrated that :Abu Hurairah, Ibn Abbas and Abu Salamah bin Abdur-Rahman mentioned the pregnant women whose husband died and she gave birth after the death of her husband. So Ibn Abbas said: "She observes Iddah until the end of the two terms." Abu Salamah said: "Rather, she is allowed when she gives birth." Abu Hurairah said: "I am with my nephew," meaning Abu Salamah.So he sent a message to Umm Salamah the wife of the Prophet. She said: "Subai'ah Al-Aslamiyyah gave birth a short time after her husband died, so she sought the judgment of the Messenger of Allah and he ordered her to get married