Sahih Muslim Book 7, Hadith Number 2763.

Chapter : Donning of Ihram for women who are in the state of menses and parturition and excellence of bath while entering into the state of Ihram.

Jabir b. Abdullah (Allah be pleased with them) reported that when Asma’ hint Umais gave birth (to a child) in Dhu’I-Hulaifa. Allah’s Messenger (may peace be upon him) commanded Abyl Bakr (to convey to her) that she should take a bath and enter Into the state of Ihram.