Hadithcore
Sahih Muslim, 1244 b
sahih

Abu Hassan reported:

It was said to Ibn 'Abbas (Allah be pleased with them) that this affair had engaged the attention of the people that he who circumambu- lates the House was permitted to circumambulate for Umra (even though he was in a state of Ihram for Hajj), whereupon he said: That is the Sunnah of your Messenger (ﷺ), even though you may not approve of it.

وَحَدَّثَنِي أَحْمَدُ بْنُ سَعِيدٍ الدَّارِمِيُّ، حَدَّثَنَا أَحْمَدُ بْنُ إِسْحَاقَ، حَدَّثَنَا هَمَّامُ بْنُ يَحْيَى، عَنْ قَتَادَةَ، عَنْ أَبِي حَسَّانَ، قَالَ قِيلَ لاِبْنِ عَبَّاسٍ إِنَّ هَذَا الأَمْرَ قَدْ تَفَشَّغَ بِالنَّاسِ مَنْ طَافَ بِالْبَيْتِ فَقَدْ حَلَّ الطَّوَافُ عُمْرَةٌ ‏.‏ فَقَالَ سُنَّةُ نَبِيِّكُمْ صلى الله عليه وسلم وَإِنْ رَغِمْتُمْ ‏.‏

References2 variants
In-Book Reference
Book 15, Hadith 227
USC-MSA web (English) reference
Book 7, Hadith 2868 (deprecated numbering scheme)