Sahih Muslim Book 22, Hadith Number 4874.

Chapter : It is not permissible for one who intends to sacrifice the animal to get one’s hair or nails cut after the beginning of Dhull-Hijja.

‘Amr b. Muslim b. ‘Ammar al-Laithi reported: While we were in a bathroom just before ‘Id al-Adha some of the persons tried to remove the hair with the help of hair-removing chemicals. Thereupon some of the people owning the bath (or some of the people sitting therein) said that Sa’id b. Musayyib did not approve of it, or he prohibited it. Then I met Sa’id b. Musayyib and made a mention of that to him, whereupon he said: O my nephew, this is the hadith which has been forgotten, and abandoned. Umm Salama, the wife of Allah’s Apostle (may peace be upon him), narrated to me Allah’s Messenger (may peace be upon him) having said as narrated above.