Sahih Muslim Book - 15, Hadith - 3009

وَحَدَّثَنِى مُحَمَّدُ بْنُ حَاتِمٍ حَدَّثَنَا بَهْزٌ حَدَّثَنَا وُهَيْبٌ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ طَاوُسٍ عَنْ أَبِيهِ عَنِ ابْنِ عَبَّاسٍ - رضى الله عنهما - قَالَ كَانُوا يَرَوْنَ أَنَّ الْعُمْرَةَ فِى أَشْهُرِ الْحَجِّ مِنْ أَفْجَرِ الْفُجُورِ فِى الأَرْضِ وَيَجْعَلُونَ الْمُحَرَّمَ صَفَرً وَيَقُولُونَ إِذَا بَرَأَ الدَّبَرْ وَعَفَا الأَثَرْ وَانْسَلَخَ صَفَرْ حَلَّتِ الْعُمْرَةُ لِمَنِ اعْتَمَرْ. فَقَدِمَ النَّبِىُّ -صلى الله عليه وسلم- وَأَصْحَابُهُ صَبِيحَةَ رَابِعَةٍ مُهِلِّينَ بِالْحَجِّ فَأَمَرَهُمْ أَنْ يَجْعَلُوهَا عُمْرَةً فَتَعَاظَمَ ذَلِكَ عِنْدَهُمْ فَقَالُوا يَا رَسُولَ اللَّهِ أَىُّ الْحِلِّ قَالَ « الْحِلُّ كُلُّهُ ».

It was narrated that Ibn Abbas [may Allah be pleased with them] said: “They used to think that Umrah during the months of Hajj was one of the greatest evils on the earth, and they would make Muaharram Safar. They would say: ‘When the backs of camel have healed and the tracks of the pilgrims have become erased and Safar is over, Umrah becomes permissible for those who want to perform Umrah. Then the Messenger of Allah (SAW) and his Companions came on the fourth (of Dhul-Hijjah), reciting the Talbiyah for Hajj, and he told them to make it Umrah. This was too hard for them, and they said: ‘O Messenger of Allah, exiting Ihram to what extent?’ he said: ‘Completely.’’”