Sahih Bukhari Volume 2, Book 26, Hadith Number 791.

Narated By Ibn Abbas : The Prophet was asked (as regards the ceremonies of Hajj) at Mina on the Day of Nahr and he replied that there was no harm. Then a man said to him, “I got my head shaved before slaughtering.” He replied, “Slaughter (now) and there is no harm in it.” (Another) man said, “I did the Rami (of the Jimar) after midday.” The Prophet replied, “There was no harm in it.”