Sahih Bukhari Volume 3, Book 38, Hadith Number 510.

Narated By ‘Aisha : I twisted the garlands of the Hadis (i.e. animals for sacrifice) of Allah’s Apostle with my own hands. Then Allah’s Apostle put them around their necks with his own hands, and sent them with my father (to Mecca). Nothing legal was regarded illegal for Allah’s Apostle till the animals were slaughtered.