The Book of Pilgrimage
وَحَدَّثَنَاهُ ابْنُ نُمَيْرٍ، حَدَّثَنَا خَالِدُ بْنُ مَخْلَدٍ، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، عَنْ حَفْصَةَ، - رضى الله عنهم - قَالَتْ قُلْتُ يَا رَسُولَ اللَّهِ مَا لَكَ لَمْ تَحِلَّ بِنَحْوِهِ .Hafsa (Allah be pleased with her) reported:I said: Messenger of Allah what is the matter with you that you have not put off Ihram? The rest of the hadith is the same
From Sahih Muslim, whose reports the scholars accept as authentic.