They used to consider performing Amra during the months of Hajj to be among the most wicked acts on earth, and they would shift Muharram to Safar, saying, "Once the camels' backs have healed, the shed hair has grown back, and Safar has ended," or he said, "and Safar has begun, then Amra becomes lawful for whoever wishes to perform it."The Prophet ﷺ and his Companions arrived on the morning of the fourth, having entered ihram for Hajj. He commanded them to convert it into Amra, and this seemed momentous to them.They asked, "Messenger of Allah, what kind of release is permitted?"He replied, "Complete release."
أخبرنا عبد الأعلى بن واصل بن عبد الأعلى قال حدثنا أبو أسامة عن وهيب بن خالد قال حدثنا عبد الله بن طاوس عن أبيه
كانوا يرون أن العمرة في أشهر الحج من أفجر الفجور في الأرض ويجعلون المحرم صفر ويقولون إذا برأ الدبر وعفا الوبر وانسلخ صفر أو قال دخل صفر فقد حلت العمرة لمن اعتمر فقدم النبي ﷺ وأصحابه صبيحة رابعة مهلين بالحج فأمرهم أن يجعلوها عمرة فتعاظم ذلك عندهم فقالوا يا رسول الله أي الحل قال الحل كله
Bukhari narrated it in the Book of Hajj, Chapter of Tamattu, Combining Hajj and Umrah, and Ifrad in Hajj, etc., no. 1564, and Muslim in the Book of Hajj, Chapter on the Permissibility of Umrah during the Months of Hajj, no. 1240, from the hadith of Wahib through this chain, and it is in Al-Kubra, no. 3795.