Sahih Muslim Book 7, Hadith Number 2937.

Chapter : Pronouncing of Talbiya and takbir while going from Mina to ‘Arafat on the day of ‘Arafa.

‘Abdullah b. ‘Umar reported on the authority of his father (Allah be pleased with them). He said: As we proceeded in the morning along with Aubs Messenger (may peace be upon him) from Mina to ‘Arafat, some of us pronounced Talbiya, and some pronounced Takbir (Allah-o-Akbar).