It is narrated from Hazrat Abu Sanabil that Sabi'ah gave birth to a child only 23 or 25 days after the death of her husband, and she began to prepare for another marriage. Someone came to the Prophet (peace be upon him) and informed him about this, so the Prophet (peace be upon him) said: If she does so, (it is fine because) her waiting period ('iddah) has ended.
Hadith Referenceمسند احمد / مسند النساء / 26471
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد ضعيف، سليمان بن يسار لم يسمع هذا الحديث من ام سلمة