Sahih Bukhari Volume 2, Book 26, Hadith Number 793.

Narated By ‘Abdullah bin ‘Amr bin Al-‘As : I witnessed the Prophet when he was delivering the sermon on the Day of Nahr. A man stood up and said, “I thought that such and such was to be done before such and such. I got my hair shaved before slaughtering.” (Another said), “I slaughtered the Hadi before doing the Rami.” So, the people asked about many similar things. The Prophet said, “Do it (now) and there is no harm in all these cases.” Whenever the Prophet was asked about anything on that day, he replied, “Do it (now) and there is no harm in it.”