Sunan Abi Dawud 1987

Narrated Abdullah ibn Abbas: By Allah, the Messenger of Allah (ﷺ) did not make Aisha perform umrah during Dhul-Hijjah but to discontinue the practice of the idolaters (in Arabia before Islam), for this clan of Quraysh and those who followed them used to say: When the fur of the camel abounds, and the wounds on the back of the camels are recovered and the month of Safar begins, umrah becomes lawful for one who performs umrah. They considered performing umrah unlawful till the months of Dhul-Hijjah and al-Muharram passed away