كتاب الحج
15  
The Book of Pilgrimage
(25)
Chapter: The pilgrim performing Qiran should not exit Ihram except when the pilgrims performing Ifrad exit Ihram
(25)
باب بَيَانِ أَنَّ الْقَارِنَ لاَ يَتَحَلَّلُ إِلاَّ فِي وَقْتِ تَحَلُّلِ الْحَاجِّ الْمُفْرِدِ ‏
Sahih Muslim 1229 c

Hafsa (Allah be pleased with her) reported:

I said to Allah's Messenger (ﷺ): 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.
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ عُبَيْدِ اللَّهِ، قَالَ أَخْبَرَنِي نَافِعٌ، عَنِ ابْنِ عُمَرَ، عَنْ حَفْصَةَ، - رضى الله عنهم - قَالَتْ قُلْتُ لِلنَّبِيِّ صلى الله عليه وسلم مَا شَأْنُ النَّاسِ حَلُّوا وَلَمْ تَحِلَّ مِنْ عُمْرَتِكَ قَالَ ‏ "‏ إِنِّي قَلَّدْتُ هَدْيِي وَلَبَّدْتُ رَأْسِي فَلاَ أَحِلُّ حَتَّى أَحِلَّ مِنَ الْحَجِّ ‏"‏ ‏.‏
Reference : Sahih Muslim 1229c
In-book reference : Book 15, Hadith 194
USC-MSA web (English) reference : Book 7, Hadith 2835
  (deprecated numbering scheme)