Sahih Muslim Book 9, Hadith Number 3554.

Chapter: Li’an (Invoking curse).

Sahl b. Sa’d reported… ‘Uwaimir al-Ansari (Allah be pleased with him) from Banu’l-‘Ajlan came to ‘Asim b. ‘Adi (Allah be pleased with him) the remaining part of the hadith is the same and it was also recorded in it: “And subsequently the separation became the practice of al-Mutala’inain.” And this addition was also made: “She was pregnant and her son was ascribed to her, and it became customary that such (a son) would inherit her and she would inherit him in the share prescribed by Allah for her.