The Book of Pilgrimage (Kitab Al-Hajj)
Muslim :: Book 7 : Hadith 2835
Hafsa (Allah be pleased with her) reported: I said to Allah's Messenger (may peace be upon him): What is the matter with people that they have put off Ihram, whereas you have not put it off after your Umra'? He said: I have driven my sacrificial animal and stuck my hair, and it is not permissible for me to put off Ihram unless I have completed the Hajj.